How do Crystals form?

An I-Search Paper

by

**********  ********

IFL 101

December 5, 2001

 

Section 1.  My Topic

Have you ever wondered why some people are fascinated by rocks?  For most people, rocks are the brown things you trip over.  For others, they are tiny worlds of wonder.  I am one such person.  Ever since I was little, I’ve been fascinated by rocks.  How are they formed?  Where do they come from?  I always came home with my pockets filled with rocks that looked or felt different.  When we went on vacation, my dad would holler about all the rocks I’d collected along the way.  By the end of a trip, the trunk would be sagging.  As I grew older, I became fascinated by crystals like amethyst, garnet, and fluorite.  I began visiting rock shops to buy crystals from around the world.  I went digging in muddy streams for sapphires in South Carolina.  I even collected agates on the beaches of Nova Scotia.  When we went home on the plane, the customs inspector asked why my suitcase was so heavy.  “Rocks!”  He gave me the oddest look and asked, “You don’t have rocks back in the States?”

 

Section 2.  What I Already Know

 

Hmmm.  It’s hard to summarize what I already know.  I know that crystals form in minerals, not rocks.  Most crystals formed deep in the earth, a long time ago.   I’ve been told that some of my favorites are associated with volcanic activity.   I know that each mineral has a specific chemical composition.  Sometimes the same mineral can have crystals in different colors and shapes.  Crystal shapes seem to be very geometric.  Some, like pyrite, even form perfect cubes.  Crystals can also be different sizes.  I’ve seen tiny quartz crystals and ones that are almost a foot long.  I’ve gotten good at identifying some minerals, but there are a lot that I still don’t know. 

Section 3.  Questions I Need to Have Answered

 

What I  really want to know is how crystals happen.  Where do they grow and why?   What makes them grow in geometric shapes?  Why are some big and others small?   Why can the same mineral have different colors?  I’d also like to learn more about different geometric shapes so I can recognize them better. 

Section 4.  The Search

Part A.   Reference Books

I started my search for reference books on the Reference page of the Schmidt Library Web.   AccessScience looked like the only science title, so I thought I’d start there.   First I typed the word “crystal” in the Search Site box.  I didn’t get anything.  Then I tried “crystals”, “minerals”, and “rocks”.  Still nothing.  I went to More Searches and searched for “crystals” in the title and the text.  I got articles on liquid crystals, colloidal crystals, and ionic crystals.  I don’t know what these are, but the excerpts didn’t look like they were what I needed.  By this point I was getting annoyed, so I thought I’d try browsing topics rather than searching.  I went to Earth Sciences, then to Geology.  Still no articles on crystals or minerals!  Closest I came were articles on caves and stalactites and stalagmites!   This online book is a pain!

 

Since I didn’t have any luck with finding reference stuff online,  I went to the reference desk at the library.   I explained my question to the reference librarian and my problems with AccessScience.  She showed me a couple of encyclopedias in the Reference Room.   The first was McGraw-Hill Encyclopedia of Science & Technology.  Weirdly enough, this is supposed to be the same thing as AccessScience!   She went to the index and showed me a bunch of listings for crystal, crystallization, and crystallography.   She explained what some of them might be about and recommended that I try volume 4 since that was where the major articles were.   She also showed me another book called the Encyclopedia of Physical Science and Technology.  She said that this would have stuff, but it would probably be more technical.   She also showed me a few other science encyclopedias and dictionaries.  I decided to look at them later.  We then went to a terminal to try AccessScience  again.  She was surprised that I didn’t get anything.  She searched for “crystal”  - just like I did – it worked!   Turns out I didn’t wait long enough for the stupid computer to respond!

 

After the librarian left, I sat down with the titles she recommended.  In McGraw-Hill Encyclopedia of Science & Technology  I found several articles with relevant information.  In the article “Crystal” (p.630), a crystal is defined as “a solid in which the atoms or molecules are arranged periodically.”  It then talks about atoms packing together to fill a space.  The article “Crystal defects” (p. 636-637) says that natural crystals are never perfect “due to the uncontrolled conditions under which they were formed.”   It goes on to say that defects that affect color can turn crystals into valuable gems like rubies.  The article “Crystal growth” (p. 643-648) looked interesting, but I didn’t really understand it.  It talked about stuff like diffusion of atoms and supersaturation.  Apparently supersaturation and heat changes how fast crystals grow.  “Crystal structure” (p. 653-660) gives a completely different definition of a crystal: “solids having, in all three dimensions of space, a regular repeating internal unit of structure.”  From this article it looks like “periodically” means a repeating pattern.  It seems that the patterns are geometric.  It also talks about the geometric patterns of some mineral crystals, but the geometry was too much for me to follow.  The article “Crystallography” (p.662-669) comes closest to what I’m interested in.  Crystallography is the study of crystals and their geometric shapes.   It says that people have been noticing the geometric shapes of crystals since prehistoric times!  This article still has a lot of heavy duty geometry, but it talks about things I recognize here and there.   I think this encyclopedia would be a good source for someone with a background in math or science.  The articles are signed by the scientists who wrote them.  You can find information about them in the index volume.  The publication date is 1997.  I think that’s current enough.

 

The reference librarian was right about Encyclopedia of Physical Science and Technology – it’s even worse.  I tried looking at articles on “Crystal growth” (p. 79-89),  “Crystallization processes” (p.91-119), and “Crystallography” (p. 121-153).  They covered the same material as the other encyclopedia, but were harder to read.  The articles were written by scientists and had scary mathematical formulas.  It looked like a calculus textbook.  The encyclopedia is current (2002) and I think the articles are good, but I need to find something easier.

 

Next, I browsed the shelf of geology resources the reference librarian recommended.  I skipped the dictionaries because I wanted more than definitions.  I decided to use McGraw-Hill Encyclopedia of the Geological Sciences.   This one wasn’t as bad as the other two encyclopedias.  I didn’t find anything under “crystals,” but  I did find articles about minerals.  “Mineral” (p.387-389) had a lot of information about mineral crystals.  Minerals are formed in four different ways: sublimation from gases, precipitation from a liquid, cooling magma, and metamorphism (p.388).   Minerals that form in magma are interesting.  Apparently as magma cools, minerals separate out and form crystals in a specific order.  Each mineral forms at a different temperature and pressure.  They can even form layers!  I also learned that sometimes crystals can change their chemical composition over time.  Occasionally they keep their old crystal shape. This is called a pseudomorph (p.389).   This encyclopedia is much better for my purposes than the others.  It even has articles on a lot of minerals I know.  The articles are still written by scientists, but at least I can understand them.  The only thing I’m not sure about is the date.  It was published in 1988.   I imagine the basics are the same, but there might be some new technical developments.

 

Part B.   General Books

I started my search for general books in the Schmidt Library Catalog.  I started by typing “crystal?” and hitting return.  I got a bunch of titles that didn’t have anything to do with mineral crystals.  So next I tried “minerals and crystal?.”  This pulled up six titles.  Two or three looked good, but they were pretty old.    There have to be more books on rocks in the library.   I remembered that we could look at the records to find subject headings.  These books used:  Mineralogy, Crystallography, and Crystals.  I decided to try again.  When I went back to the search screen,  I noticed that there were two options for searching, specific searches and keyword.  I guess I was just doing a keyword before.   This time I tried “Crystallography” and pressed the button for a specific subject search.  Pay dirt!   The subject heading “Crystallography” lists 31 titles!   Several of the titles had possibilities, so I wrote down some call numbers.  There was even a book from 1992 – unfortunately, the Catalog said it was checked out.    “Crystallography” had cross-references to “Crystals” and “Mineralogy,” so I checked those headings out too.  Some new titles came up, so I wrote down a few more call numbers.   “Crystals” had a cross-reference to “Crystal growth.”   There were two titles there.

 

I took my list of titles and call numbers to the second floor.  I started with the crystallography titles.  Most of those were in QD 911-921.  A lot of them were pretty old.  Many claimed to be basic introductions – more formulas.  Finally, I picked two that were slightly more recent (1971 and 1990) to look at further.  The books on crystal growth weren’t on the shelf.  The books on mineralogy were in QE 364-372.  The books were still old, but at least looked like they were in English.  I wanted to take some of these home too, so I did some browsing to find interesting ones.   I ended up checking out several guide-type books and a few with pictures of mineral specimens. 

 

The books I took home all had bits of information that answered my questions, so it was hard to decide which were the best.  Let’s start with the ones I didn’t use.  I ruled out two books on crystal geometry and chemistry.  They both looked good, but they would have taken a long time to wade through.  I don’t really have enough background in chemistry or geometry.  I also decided not to use several popular books on minerals and crystals.  They had nice pictures of some mineral crystals I hadn’t seen before, but they didn’t focus enough on my questions.  In the end, I picked three books as the best. 

 

The first book is Peterson’s Rocks and Minerals.  I see the Peterson Field Guides in bookstores all the time, so they must be pretty common.   This one was written by Frederick Pough,  a former Curator of Geology and Minerals at the American Museum of Natural History.  It was also the most recent book I found – published in 1995.   This book has a section on mineral environments (p. 37-41) that explains how mineral crystals occur.  As magma cools it forms a granite pegmatite dike that can have a lot of different crystals in it.  Beryl, fluorite, quartz, topaz, and calcite can all form in this environment.  When cooling granite cracks, it forms fissures.  Gases and hot liquids with dissolved metals can move through the fissures.  Once the fissures cool, they can have crusts of tiny crystals or become veins of ore.  When you find crystals loose, it is usually because of weathering.  Water dissolves the rock and carries the crystals away.  Weathering can also change the chemistry of minerals and change them into something else.   Other minerals, like salt and gypsum can precipitate out of water.  Some crystals like garnet are associated with metamorphic rocks (ones that were subjected to heat and pressure to change them).    This book also talks about the color of crystals (p. 42-43).   I thought the colors had to do with the chemicals in the minerals.  It does, but it was more complicated than I thought.  Some minerals do have a consistent color because of their chemical makeup.  Most minerals occur in a variety of colors.  This happens because the minerals can contain many different impurities which alter the color. 

 

This book also has a whole chapter on crystal classifications (p. 53-70).  It finally explains the crystallography information I found in the reference books.  Crystals are grouped into 6 systems: cubic or isometric, tetragonal, hexagonal, orthorhombic, monoclinic, and triclinic.  Each system is distinguished by the relative lengths of their vertical and horizontal axes,  and by the angles between them.  For example, a cube has three axes that are of equal length and at right angles [p. 57].   A hexagonal crystal has a vertical axis that is at right angles to three horizontal axes (p. 59).  The 6 systems are actually broken down into 32 classes, but most people find them difficult (p.54).  The chapter goes on to talk about more complex crystal forms like twinned crystals and crystals that combine more than one geometric shape.  Most of the book talks about how to identify individual mineral specimens.   This is very useful.   For each mineral they have descriptions, drawings of crystal forms, and color pictures!   I think this would be a good book for any mineral collector.

 

The second book I chose was Mineralogy for Amateurs by John Sinkankas.  He didn’t have a career in mineralogy, but he got help in writing his book from a number of experts.  He wrote the book because popular books were too elementary and college texts were too difficult for people without backgrounds in chemistry, mathematics, and physics (p. ix).   His book is written at a level in between the two.  The first half of the book has chapters on things like atomic structure, mineral classification, crystal growth, crystal geometry, physical properties, specific gravity, optical properties, formation, and identification.  The second half of this book has descriptions and pictures of different minerals.  The book also has a bibliography, but since the book was written in 1964, I doubt that I could find many of them.   I learned the most from the section on crystal growth.   A crystal starts as a small seed cluster of atoms and grows outward, layer by layer (p. 60).  The crystal continues to grow as long as there are atoms to feed it (p. 60).  Crystals also grow at different rates in different directions (p. 63).  They can also grow at different rates at different times because of changing conditions (p. 65).  This explains why no crystals are perfect!  Sinkankas even says that changes in growth rate can cause a fluorite crystal that starts as a cube to turn into an octahedron, or vice versa! (p. 66)   This explains why crystals can combine more than one geometric shape.  For instance, a garnet can combine a dodecahedron and a trapezohedron (p. 535).  I’m amazed by how many odd things can happen when crystals grow!   I also learned that the physical structure determines how a crystal can be broken.  It’s called cleavage (p. 162).  I have green and purple fluorite crystals that I thought were naturally occurring octahedrons.  Turns out they were probably cleavages from a larger crystal (p. 163).  

 

Mineralogy for Amateurs also has some information about crystal colors.   I learned some new terminology.  Idiochromatic minerals are minerals that have an innate color because of their chemical makeup (p. 198).  Malachite and azurite are idiochromatic (p. 199).  Colorless minerals that take on different colors because of impurities are allochromatic (p. 199).  Quartz, which can be purple, yellow, smoky, or clear, is allochromatic (p. 199).  I  learned that you can change the color of some crystals by heating them or exposing them to radiation (p. 201).  Usually it either makes them darker or lighter.  I also learned that some crystals turn spectacular colors under ultra-violet lights – this characteristic is known as fluorescence or photoluminescence (p. 203).   This book was very readable – I wish there was a newer edition with color pictures.

 

For my third book, I chose Dana’s Manual of Mineralogy by Cornelius Hurlbut, Professor of  Mineralogy at MIT.  The copy we have is the 18th edition from 1971.   According to the preface, this is designed to the text for a beginning course in mineralogy (p. v).   Since this book has been through so many editions, it’s probably a standard text.  It would be interesting to know if it is still being published.  1971 is pretty old.   The pictures weren’t even in color.  This book covers the same topics as the other two, but makes it even more complex.  For instance, it explains the Hermann-Mauguin symbols for describing crystal classes (p.16-18),  and also the Miller indices which “express the intercepts of crystal faces upon the crystal axes” (p. 22).   To be honest this one is beyond me again.  I think this is a good book, but I’d want to have a geometry class first!  One thing I did like about it was the descriptions of individual minerals and their characteristics.  They were more detailed than those in other books. 

 

In class, we learned about other places to look for books so I thought I’d check a few out.  I was curious to see if the Dana book was still being used, so I searched Amazon.com  for “Dana’s manual of mineralogy”.   I found out that a paperpack copy of the 21st edition was published in 1993.  It has a CD-Rom with pictures of minerals and information about them.  It costs almost $100.  I don’t think I’ll be buying one anytime soon!   Amazon.com has an option to search for other books with the same subject headings, so I put checkmarks next to Mineralogy and Crystallography.  A lot of the books listed as being out of print, but I found references to a few newer books.  I wrote down the authors and titles so I could look for them in other libraries.  To look for books in other libraries, I decided to look at the ACLCP Internet Catalog.  Our professor said that was a good place to find books that we could get through Interlibrary Loan.  This one searches different from our catalog.  I used the pull down menus to create search that said “Find subjects that begin with the words mineralogy.”  Mineralogy had over 300 titles.  I scanned the alphabetical list for books with more recent dates.  Most were older, but I did find a few.  One library had the Dana  book I found in Amazon.com.  I even found a few titles published in 2000.      

Part C.   Popular Magazines and Scholarly Journals

 

I started my search for articles in Expanded Academic ASAP.  My professor said that it uses the same subject headings as the online catalog, so I decided to try both “crystallography” and “mineralogy” as subject searches.  I started with crystallography.  I got 577 articles, but most didn’t have text, so I decided to limit to full text.  That cut it down to about 100 articles.  Most of the articles were so technical that I didn’t even understand the titles.   I’m amazing that so much research is going on.  I thought that people would know about crystals by now.  Mineralogy had much better results.  There were articles about museums, mineral shows, the history of mineral collecting, and different minerals.  One article, “Secrets under the ‘scope’” by Quintin Wight caught my eye because I never thought about using a microscope to examine crystals.    It turns out there is a whole area of collecting called micromounting.  These are minerals specimens with crystals so small that they can only be seen under a microscope.  The author’s reasons for collecting tiny crystals taught me some things about crystal growth that I didn’t know.   First, there are some minerals that only form crystal that are too tiny to see without a microscope.  He also says that smaller crystals come closer to having perfect forms.  Since they don’t grow long and aren’t as affected by environmental factors, they are less likely to be misshapen.  Lastly he says that you can learn more about your crystals:  “The microscope reveals minute inclusions, tiny surface changes, vicinal faces, faint twinning lines, and other features not necessarily visible on a macro scale.”   This article is hard to evaluate because there isn’t a lot of information.  The author seems to be a collector.  He also has written other articles on micromounting, so he should be an expert.  I don’t know anything about the magazine Rocks & Minerals, but it looks like it’s popular. 

 

Even though the articles under Mineralogy were interesting, I had trouble finding ones that answered my questions, so I decided to try some keyword searching.  My first search was “crystal* and form* and mineral*. ”   With this search I found an article by John S. White called “A New Twin Law, or What?”   This article talks about twinning, a process where two crystals grow attached to each other.  Apparently there are a number of different types of twins that grow according to different “laws.”  Even more interesting, the experts haven’t figured out what all the laws are yet!   The article describes specimens of unusual twins and tries to guess how the crystals might have grown.  The frustrating thing is that the article on the computer doesn’t include any of the pictures that the author is describing!!!!   Unfortunately, York College doesn’t have the magazine Rock & Minerals, so I can’t see a paper copy.  I don’t think Interlibrary Loan would be good because the photocopy wouldn’t be in color.  Darn!  The article was a real good one too!  The author is a former curator at the Smithsonian mineral department.  The article even has footnotes.    

 

I next searched for “crystal* and grow*” to see if I could find more articles about how crystals grow.  I actually got over 300 articles with this search.  Apparently, scientists are doing a lot of research into growing crystals in laboratories.   An article from Electronic Engineering News  had the title, “Record touted in crystal growth.”  Since I now know that some crystals are microscopic, I’m curious about how big crystals can grow.   This article was a short news article with no author, but it was very interesting.  In Lawrence Livermore National Laboratory, scientist used an infrared laser and a high pressure tank of potassium dihydrogen phosphate solution to grow salt crystals.  They were able to grow a 701 pound crystal in 52 days!    From this search, I also found a popular article in Earth called “Crystal clear.  It did provide some details that I hadn’t found before.   I learned that the time needed to form crystals varies greatly.  Some crystals can form in hours; others take millions of years.  The size of crystals can also be affected by the amount of space they have to grow.  If a crystal grows in a gas bubble or a fissure in cooling magma, it has more room.  Crystals can also be very fussy about conditions in which they grow.  Diamonds require great heat and pressure.  I guess that’s why they are rare.  I couldn’t find any information about the author or the magazine, but I suspect they are popular.  The article might have even been written with kids in mind – it talked about growing sugar crystals in water.   Another interesting article was “Impurities clock crystal growth rates” from Science News.  It talks about research done with quartz crystals by Phillip D. Ihinger and Stephen I. Zink at Yale University.  By examining a crystal, they can actually determine its growth history.  As crystals grow, impurities are absorbed into their faces.  When crystals are growing fast, they usually have more impurities.  They think their research will help scientist grow crystals with less imperfections.   This news article doesn’t have an author, but it is talking about real research.  It also referred to a longer article published in Nature.   I wrote down the Nature citation so that I could look for it later.   Next I tried “crystal* and color*”.  No luck.  “Crystal* and systems”.  No luck.    I tried looking for another index to use.  I tried Ingenta.  A search for “crystals and color” actually retrieved some interesting citations about studying color and changing it with radiation.  I clicked on Article Availability for one.  It asked me to fill out a form, so I did.  Then it told me the article would be $31 – forget that!

 

After I finished searching, I checked the Schmidt Library Catalog for Nature.  We do have it; the article I needed was on microfilm.  “Determination of relative growth rates of natural quartz crystals” is by Phillip D. Ihinger and Stephen I. Zink at Yale University.  The article goes into more depth about the research they did on quartz crystals.  They actually took a clear crystal from Brazil and cut cross sections out.  They then took spectroscopic measurements of the cross sections.  The science was pretty high level, but it sounded like they could read the cross sections like rings on a tree.  They were able to tell a lot of things.  They learned that all faces of the crystal don’t grow at the same speed.  They also learned that the overall growth rate varied over time.  When crystals grow faces, they absorb more impurities.  They described the impurities in clear quartz crystals as “hydrogen-bearing species” (p. 865). I also learned that a lot of what scientists say about crystal growth is actually theories; they don’t have a lot of laboratory research to back it up.   They even go on to say,  “The actual mechanisms responsible for the variation in size and shape of individual crystal faces are, in fact, not well understood.”  (p.856).  This article was very scholarly and has many footnotes and figures.

 

I have the feeling that there are other articles out there somewhere, but I can’t figure out how to search for them.  Part of the problem is the fact that I’m not searching for specific mineral crystals.  I think that would be easier.  Most of the research is being done about specific minerals.  All in all, I found searching for periodicals very frustrating.  I found interesting articles, but a lot weren’t focused on my questions.  I also had to wade through screens and screens of results to find the articles I used.  

Part D.   Newspapers

 

I really was apprehensive about searching for newspaper articles about my questions.  After all, how many times do you find articles about rocks in your local paper?  Since I had to do this part anyways, I went to Lexis-Nexis Academic Universe.    The News part of this index has several sections, but not one on science.  I decided to try “General News.”  I started by searching the keywords “crystal* and growth.”  I changed the date option to “all available.”   Yuck!  I got almost 800 articles, but couldn’t tell how most of them related to my search at all!  The only obvious ones had “crystal ball” in the title.  Next I searched for “crystal* and growth and mineral*”.   This time I got 8 articles, but I got things like “the perfect chocolate” and “life on Mars.”   I don’t get this index.  I looked at the help file.  For one thing, I should have been using an “!” as a wildcard.  It also looks like the “and” should be “AND.”  I tried changing my search to match.  Didn’t make a difference.  Oh well…    Next I tried “mineralogy.”  I got a lot of obituaries for mineralogists.  After going through several screens,  I did find an article in the New York Times called “Giant Black Diamonds Of Mysterious Origin May Hail From Space”.   This one was worth digging for!  It turns out there are giant black diamonds called carbonadoes.  Some are as big as baseballs.  They don’t cleave (break) like regular diamonds and their structure is slightly different.  Testing suggests that they are 4 billion years old.  Scientist don’t know how they formed; some scientists think they came from asteroids that bombarded the earth a long time ago.   Next I tried searching for “crystallography.”   I found more obituaries and articles about proteins and bacteria.  It sounds like there are crystals involved with biology too.  No articles for me, though. 

 

Since I was having so much trouble finding newspaper articles, I asked my professor for help.  She recommending trying an online index for science news called UniSci.    The first time I tried it,  the page wouldn’t come up.   It didn’t work the next few days either.  Eventually I did get in.   It asks you to search for single words, so I tried “mineralogy”, “crystallography,” “minerals,” and “crystals.”  “Mineralogy” only retrieved a single article.  “Crystallography” had a lot of hits, but they were mostly biological.  “Minerals” and “crystals” both retrieved interesting articles.  

 

The first article I chose was “Diamond Duo Sheds Light On Internal Earth Pressure.”   This talked about a diamond crystal that had a microscopic piece of coesite inside.   Diamonds form under intense pressure deep in the earth, but scientists didn’t really know how much pressure.  As diamonds travel upward toward the surface, the pressure decreases.   Since the coesite was trapped inside the diamond crystal, it would have kept the same pressure level on the trip up.  Scientists from the Carnegie Institute and Russia used x-rays and lasers to test the coesite.  They found that it formed at a pressure of  3.2 gigapascals.  3.2 gigapascals equals 464,121 pounds per square inch!

 

The second article I chose was “Hawaiian Lava Clue To 3 Billion Year Old Komatiites.”   Komattites are lava flows that occurred at least 3 billion years ago.  They are similar to more recent lava flows except for a few things.  They have high concentrations of the mineral nickel.  They also can have crystals of olivine, pyroxene, or plagiocase that are 3 feet long and ½ an inch wide!

 

I chose one last article, “First Images Of Crystal Nucleation Are Unexpected.”  This one was the best!   Scientists at University of Alabama used an atomic force microscope to look at the first molecules that form in the center of a crystal.  All the books I looked at said that this seed in the center of a crystal is a tiny version of the crystal shape.  It grows by adding layers to the outside.  These scientists proved that everyone was wrong about the shape of the seed crystal!  The first molecules actually form a flat sheet.  Additional sheets are then added.  The tiny crystal doesn’t look like the larger crystal until about 200 molecules are present. 

 Part E.   Internet

 

I started my search on Google, my favorite search engine.  Since the Internet doesn’t use subject headings, I thought I’d start by searching the phrase “mineral crystals.”   I found a lot of sites.  There were so many, I decided to send myself links in email so I could look at them later.   I also searched for “mineralogy” and “crystallography.”  Mineralogy was a good search, but crystallography had too many high-end technical sites.  Next I tried searching for “crystals color.”  That was a bad search.  I forgot that “crystal” can also be glassware.  “Minerals crystals color” worked much better.  I also tried “minerals and crystal growth.”   I found enough web sites in Google, but I decided to try a couple other search engines out of curiosity.  I went to AskJeeves  and asked “Why do crystals come in different shapes, sizes, and colors?”  The first two responses Jeeves came up with were “How do I color my hair?” and “Where can I learn about the alternate treatment modality crystal therapy?”  Yeah, right.  To be fair, they did have a link for “Where can I learn about rocks and minerals?”  It went to a page at the Franklin Institute with some decent links (http://www.fi.edu/qa97/spotlight1/spotlight1.html).  I also tried the WebBrain search engine we looked at in class.  I typed “mineralogy” which actually took me to the heading “soil mineralogy.”  From there, I clicked on “minerals.”  Minerals gave me some related headings that looked pretty good:  Databases; Directories; Mineralogy > Education; and Crystallography >Education.  I actually found a site that I missed in Google.

 

I ended up looking at a lot of web pages.  It was nice to finally see color pictures of some of the crystals I was reading about in the books and journal articles!   It was hard to decide which ones were the best web sites.  I ended up clicking on a lot of links.   I finally decided on 6 sites.    The first site I chose was “Introductions to Crystallography and Mineral Crystal Systems” by Mike and Darcy Howard.  Mike Howard is a geologist.  Darcy Howard is a scientific illustrator.  This is the best explanation of crystal systems that I’ve found.  He takes the concepts and explains them step by step in English.  There is a chapter for each crystal system with good line illustrations of the different crystal forms.   I think if I spend some time with this, I’ll eventually be able to recognize some of the harder geometric shapes.  The chapters are hosted by Bob’s Rock Shop.   This is just a popular site, but it includes a lot of good links for rockhounds. 

 

Since I knew that crystals could be very tiny, I decided to find out how big they can get.  I found this in a web article called “Largest Mineral Crystals on Record” by John Bett.  He summarized the information from a 1981 article in American Mineralogist.    The largest crystal size varies from one mineral type to another.  The largest crystal was a beryl from the Malagasy Republic.  It was 18 meters long and 3.5 meters in diameter.  They guessed that it weighed about 380,000 kilograms.  That translates to 837,756 pounds!   I only used this source because it had information I didn’t find anywhere else.   John Bett is a dealer who sells very expensive mineral specimens.  He does provide some general information about minerals, but he mostly wants to sell stuff.

 

Since I was interested in what causes mineral colors,  I also chose the Mineral Spectroscopy Server from the California Institute of Technology.  The site is run by George Rossman, a Professor of Mineralogy.    According to the front page,  the site is “is primarily dedicated to providing information about color in minerals and access to data on Mineral Absorption Spectra in the visible and infrared regions of the spectrum and Raman spectra of minerals.”   This site explains that color in minerals has five causes:  “metal ions, intervalence charge transfer, ionizing radiation, physical effects, and band gaps.”   It also gives lists of minerals for each type with the substance that causes the color change.  For instance, the green color in emeralds is caused by Cr3+ ions.  Fluorite turns purple when exposed to gamma rays.  Labradorite changes colors in light because of refraction.  Since this information was gathered in a mineralogy lab, I think it’s an excellent source of information.  They also seem to update the site frequently!   

 

I also decided to pick some comprehensive mineralogy web sites so that I could continue learning about minerals.   The best mineral database I found was Mineralogy Database by David Barthelmy, a petroleum geologist.    The database has 4,255 minerals.   I didn’t know there were that many!   He lists an incredible amount of information for each mineral: chemical formula, composition, empirical formula, IMA status, locality, name origin, axial ratios, cell dimensions, crystal systems, cleavage, color, density, diaphaneity, fracture, habits, hardness, luminescence, luster, streak, optical data, Dana class, Strunz class, bibliographic references, and related web links.  For many minerals he even has images, a sound file with the name pronunciation, and rotating 3-D images of the crystal form! 

 

Another mineralogy database is mindat.com.   This database is even larger with 10,064 minerals.  It has less information about individual minerals and is harder to use.  It does have some features that Mineralogy Database doesn’t – it has extensive lists of synonyms, varieties of minerals and locations.  I’m not sure how reliable all the information is - a lot of it is contributed by collectors.  I couldn’t find anything about the author either.   Many minerals seem to be new varieties that haven’t been approved by the International Mineralogical Assocation.  I think the most useful information is the localities.  I typed in Pennsylvania and learned about what minerals are available in different counties and mines.  This site also has message boards and a chat room.  I think it would be a good site for rock hounds who want to do collecting.

 

I think the best site for finding more sites on mineralogy is Links for Mineralogists from the Institute of Mineralogy, University of Würzburg.  This is a directory of links “for mineralogists, petrologists, crystallographers, geologists.”  It seems to be updated frequently.   The links are arranged in different categories and subcategories, just like Yahoo!.   You can even search them.  When you get to a list of sites, each site has a brief description.  Many of them are scholarly.   I wish I had found this earlier in my search, it would have saved me a lot of time looking for sites.

 

Section 5.  What I Learned

 

I’ve found the answers to my questions, but I’ve learned that the answers weren’t as simple as I thought they’d be.  Crystals form in specific shapes because of their chemical formulas.  Certain molecules only fit together in specific patterns.  These patterns result in 6 crystal systems with 32 separate classes.  The individual classes are described using very complex concepts of three dimensional geometry. 

 

Crystals mainly are different colors either because of optical properties or chemical impurities present while they form.  This isn’t as simple as it sounds either, scientists are studying optical properties of minerals using all sorts of state of the art equipment.  

 

Size of crystals depends on a lot of factors: the type of mineral, the amount of space to grow, the available amount of material, temperature, and pressure.   Scientists have a general idea about how most crystals grow, but it happened millions of years ago deep in the earth, so they don’t have a perfect understanding.  Some scientists grow crystals in labs so that they can experiment with different growth conditions and see how they affect growth.  Crystals formed in the earth may look perfect to the naked eye, but no natural crystals are perfect.  Their uncontrolled environments cause them to grow at different rates and cause a variety of imperfections.  This makes each crystal unique.

 

I was surprised by how hard it was to do research about my questions.  It was easy to find answers, but almost impossible to understand them!   I wanted to use scholarly materials, but even the basic texts in mineralogy and crystallography were a tough go.  I didn’t have the right background.  Much of what I found in periodicals described advanced scientific research performed on specific minerals.  I really need a better background in geometry and chemistry.   I ended up having to use more popular sources than I wanted.  I was surprised by the level of knowledge that even an amateur mineralogist needs.  I thought I knew a fair amount about minerals, but I haven’t even scratched the surface. 

 

When I have time, I’m going to try to learn more about mineralogy.  For starters, I want to learn how to identify the different crystal classes when I see them in specimens.  I want to be able to tell the difference between a trapezohedron and a dodecahedron, or a hexagonal trapezohedral and dihexagonal bipyramidal.   I also want to go back and relearn the periodic table of elements so that I can translate chemical formulas and begin learning the different families of minerals.  But first, I’m going to take a break.  After a whole semester, I’m tired of doing research!  J

Section 6.  Bibliography  

 

Barthelmy, David.  Mineralogy Database.  2001.  28 Nov. 2000 < http://webmineral.com/>

Betts, John.  “Largest Mineral Crystals on Record.”  John Betts Fine Minerals.  1999.  28 Nov. 2000 < http://www.johnbetts-fineminerals.com/jhbnyc/articles/bigxls.htm>

Broad, William J.  “Giant Black Diamonds Of Mysterious Origin May Hail From Space.”  New York Times.  17 Sep. 1996, late ed.:  C1.  Lexis-Nexis Academic Universe.  21 Nov. 2000  <http://www.lexisnexis.com/universe>

“Diamond Duo Sheds Light On Internal Earth Pressure.” UniSci.  17 Oct. 2000.  25 Nov. 2001. <http://unisci.com/stories/20004/1017002.htm>

“First Images Of Crystal Nucleation Are Unexpected.”  UniSci.  3 Aug. 2000.  25 Nov. 2001. < http://unisci.com/stories/20003/0803004.htm>

“Hawaiian Lava Clue To 3 Billion Year Old Komatiites.”  UniSci.  05 Oct. 2000.  25 Nov. 2001.  < http://unisci.com/stories/20004/1005003.htm > 

Howard, Mike and Darcy.  Introduction to Crystallography and Mineral Crystal Systems.  Bob’s Rock Shop.  Jan. 2000.  28 Nov. 2000 < http://www.rockhounds.com/rockshop/xtal/ >

Hurlbut, Cornelius S., Jr.  Dana’s Manual of Mineralogy.  New York: John Wiley & Sons, Inc, 1971.

Ihinger, Phillip D. and Stephen I. Zink.  “Determination of relative growth rates of natural quartz crystals.”  Nature 404 (2000): 865-868. 

Kelber, Klaus-Peter.  Links for Mineralogists.  14 Oct. 2000.  Institute of Mineralogy, University of Würzburg.  28 Nov. 2000 < http://www.uni-wuerzburg.de/mineralogie/links.html>

Peterson, I.  “Impurities clock crystal growth rates.”  Science News.  22 Apr. 2000: 263.  Expanded Academic ASAP.  14 Nov. 2000 <http:// infotrac.galegroup.com >

Pough, Frederick.  Rocks and Minerals.  Boston: Houghton Mifflin Company, 1996.

Ralph, Jolyon.  mindat.com.  2001.  28 Nov. 2001 < http://www.mindat.org/>

Rosssman, George R.   Mineral Spectroscopy Server.   26 Nov. 2000.  California Institute of Technology.  28 Nov. 2000 < http://minerals.gps.caltech.edu/>

Scovil, Jeff.  “Crystal clear.”  Earth.  Apr.1997:  58-59.   Expanded Academic ASAP.  14 Nov. 2000 <http:// infotrac.galegroup.com >

Sinkankas, John.  Mineralogy for Amateurs.  New York: Van Nostrand Reinhold Company, 1964.

Wight, Quintin.  “Secrets Under the 'Scope.”  Jul. 2000: 268.  Expanded Academic ASAP.  14 Nov. 2000 <http:// infotrac.galegroup.com >