THE MINERAL GYPSUM


Gypsum is one of the more common minerals in sedimentary environments. It is a major rock forming mineral that produces massive beds, usually from precipitation out of highly saline waters. Since it forms easily from saline water, gypsum can have many inclusions of other minerals and even trapped bubbles of air and water.

Gypsum has several variety names that are widely used in the mineral trade.

Crystals of gypsum can be extremely colorless and transparent, making a strong contrast to the most common usage in drywall. The crystals can also be quite large. Gypsum is a natural insulator, feeling warm to the touch when compared to a more ordinary rock or quartz crystal. Sheets of clear crystals can be easily peeled from a a larger specimen.

Gypsum crystals can be extremely large - among the largest on the entire planet. A cave in Naica, Mexico contains crystals that dwarf the people inside. Apparently, ideal conditions for the slow growth of gypsum were maintained for thousands of years, allowing a few crystals to grow to enormous sizes. Click on the photos for larger images, and see this abstract for an article in the April 2007 Geology magazine that describes how the growth of these gypsum megacrystals occurred.

Plaster of Paris is made by heating gypsum to about 300 degrees Fahrenheit, driving 75% of the water out of the mineral.  This reaction absorbs energy, enabling a sheet of drywall to resist fire for a while. Heating further to about 350 degrees F drives out the remaining water and results in conversion to the mineral anhydrite.

PHYSICAL CHARACTERISTICS:

 

Google
 

Copyright ©1995-2008 by Amethyst Galleries, Inc.
Site design & programming by galleries.com web services