Glen Evans:
The Compleat Naturalist
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CALCITE and QUARTZ

Many beautiful geological specimens exist in the collections of the Museum as a result of Glen Evans' keen eye.

 

Calcite
TMM3363 Calcite scalenohedrons TMM3363 Calcite (scalenohedron_close up)

Specimen: TMM 3363
Mineral: Calcite (scalenohedrons)
Collector: Glen Evans

Specimen: TMM 3363
Mineral: Calcite (rhombohedral crystal)
Collector: Glen Evans

TMM3363 Calcite (rhombohedron)

Calcite (calcium carbonate)

This example is a stalactite from a cave in Texas.  The calcite is precipitated from ground water as that water emerges into caverns.

Specimen is part of the Museum Mineral Education collection.

Image is about only one third of the original stalactite measuring about 2 feet in length.

Calcite (Stalactite)
TMM3379 Quartz (amethyst)

Quartz

Specimen: TMM 3379
Mineral: Amethyst (Quartz) 
Locality: Arizona
Collector: Glen Evans

Specimen is about 4"x6"

Quartz (silicon dioxide) is colorless, but occurs in nature in many colors! Violet colored quartz is called amethyst, and the color may result from impurities of iron in the crystals. Smokey quartz, yellow-brown to black in color, is attributed to free silicon formed by exposure to radiation.


Copper ore and unusual 'finds'

Copper ore (malachite and chalcocite) Lava (black vesicular)

Specimen: TMM1064
Mineral: Copper ore (malachite and chalcocite)
Locality: St. Elmo Mine, Hudspeth County, Texas
Collector: Glen Evans

Specimen: TMM3401
Rock type: Lava, black vesicular
Locality: Padre Island, Texas
Collector: Glen Evans, April 1948

How did a volcanic rock arrive on Padre Island???

  more on all these specimens