Minerals

WHAT IS A MINERAL?

A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties.  By comparison, a rock is an aggregate of minerals and/or mineral-like substances that do not demonstrate crystallinity and do not have a specific chemical composition.  Minerals range in composition from pure elements and simple salts to very complex silicates with thousands of known forms.

Amazonite Galena
Amethyst Halite
Azurite Okenite
Fluorite  

Amazonite - Coming Soon


Amethyst – Simple But Sensational

Minerals which produce both attractive mineral specimens and gemstones usually represent a complicated combination of natural elements or are quite rare, or both.  Amethyst, however, is neither, being a variety of quartz [Si02], chemically one of the simplest of minerals, and reasonably common in occurrence.  Amethyst ranges in color from pinkish-violet to dark purple, sometimes with red or blue secondary hues, these colors being derived from minor iron impurities within the quartz.  Because of its considerable hardness and resistance to breakage, amethyst, like all quartz gems (rock crystal, citrine, rose and smoky quartz, etc.), is quite suitable for jewelry applications.

Amethyst is found in a variety of environments, but tends to be associated with rocks form from magma, typically basalts.  The most famous amethyst-producing area in the world is in Minas Gerais state in Brazil, where groundwater has deposited purple amethyst crystal linings in tubular and spherical openings in basalt flows.  Similar deposits further southwest in Brazil and neighboring Uruguay have similar basalt-hosted amethyst, often of very dark purple color.  Amethyst is found and mined in some quantity on every continent, with Thunder Bay, Ontario being the largest producing area in the North America, also in association with ancient basaltic rocks.  Amethyst is found at a number of localities, particularly in eastern North America, in coarse-grained granites known as pegmatites, also of magmatic origin.

(Large specimen from Minas Gerais, Brazil; smaller specimens from, left to right; Casas Grandes, Mexico; Kingston Range, California; Veracruz, Mexico; Diamond Hill, South Carolina; South Africa)


Azurite - Coming Soon


Fluorite - Coming Soon


Galena -Coming Soon


Halite - Coming Soon


Okenite – Unusual and Unusually Pretty

Okenite [CaSi2O5·2H2O] is a mineral closely associated with the zeolites, which are hydrated calcium and sodium aluminum silicate minerals commonly found in association with basalt lava flows.  Like the zeolites, okenite is formed when groundwater rich in calcium and silicon migrates through lava flows, and due to changes in water chemistry and/or temperature eventually deposits these minerals in cavities within the basalt.  Okenite was first described from Disko Island, Greenland, and named for German naturalist Lorenz Oken.

Perhaps the most common and spectacular source of okenite is from the Deccan basalts, a great stack of 60-65 million year old lava flows in western India.  The okenite there is often deposited on a rind of previously-deposited zeolite material or chalcedony, coating the inside of gas-bubble cavities.  The okenite crystallizes as snow white, needle-like crystals in round clusters which resemble cotton balls.  Okenite is often associated with the zeolites apophyllite [(K,Na)Ca4Si8O20(F,OH)•8H2O], gyrolite [Ca2Si3O7(OH)2•H2O] and prehnite [Ca2Al(AlSi3O10)(OH)2].

The fibrous okenite crystals are somewhat flexible but also fragile and splinter-like, which means that petting, or dusting, okenite is not a good idea.  Okenite is best cleaned with a compressed air sprayer (as used for computers) sprayed from far enough away to prevent damage to the crystals.