Quartz Crystals

 

 

Who doesn't enjoy seeing a cluster of sparkling crystals and wondering about the miraculous environment that must have created them?  Or perhaps marveled at a man-sized crystal of a mineral that has existed intact through untold years?

The leap of knowledge between simple appreciation or curiosity about crystals and a thorough understanding of them is a mighty one.  This is often a stumbling block for many beginning gemologists.  Unless you have a pretty good working knowledge of physics, many of the terms and principles involved will be new and require serious and prolonged study.  With that caveat, and recognizing there is no way to teach the subject in a one-page paper, we can discuss some of the main ideas and at least provide a beginning point for your study of crystallography.

A crystal is an orderly collection of units in a solid.   A way of thinking about this might be to consider a mound of loose bricks, coke cans, flower pots, etc... scattered every which way.  That would represent a rock. It looks like a big lump of something but is actually a collection of unique random items.   When the bricks are removed and laid out in a repeating, orderly pattern, (a wall), that would represent a crystal.

There are 7 main systems (groups) of crystal families. Imagine our wall again.  If the bricks are rectangular, there are a lot of ways you can regularly stack them- vertically, horizontally, two horizontal and one vertical, etc... but in most cases, the overall outward appearance will be squarish or rectangular.

In a likewise manner, a wall made from hexagonal bricks will tend to exhibit characteristics of that building block.   If we understand that, we can understand that the exterior shape of a crystal will often reflect the shape of the units from which it is created.  If we identify the exterior form, it can help us to identify the gem material. Most gem materials will be in the cubic or hexagonal systems and for brevity, we'll focus on those two.

The cubic system contains Diamonds, Garnets, Spinel, Fluorite, and others.  Common hexagonal crystals include Sapphires, Rubies, Emeralds, Amethyst, Citrine, and Calcite.  If a gemologist is lucky enough to encounter these gems as uncut crystals, it is often easy to identify the structure and narrow the list of possibilities visually.  Gems that are faceted, that is mechanically formed into the familiar shapes we use in jewelry, will need to be examined with tools that measure the way light interacts with the structure of the crystal on a microscopic level.  The exterior of the crystal has changed into a faceted shape, but the interior is intact and we are able to test it. Important diagnostic tools for this step are the Refractometer, Dichroscope, and Polariscope which are discussed separately.  Click on any of the links above for more detailed information.

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