quartz, variety Microcrystalline

Description: Quartz is the most abundant mineral found at Earth's surface, and its unique properties make it one of the most useful natural substances. It occurs in many forms; in microcrystalline form it is called chalcedony. In the gem trade, the name chalcedony usually describes only white or blue varieties, to distinguish it from the multicolored banded variety Agate and other unique variations (including chert, red jasper, carnellian, novaculite, and flint

Chemical Formula: SiO2

Crystal Form: none, microcrystalline quartz occurs in botryoidal, mammilary, stalactitic, massive, nodular forms, as smooth rounded pebbles, as banded masses, as amygdules, and as the linings of geodes.

Crystal System: Hexagonal

Color: Varieties are colorless, purple, rose, red, black, yellow, brown, green, blue, orange, etc.

Streak: Colorless (harder than the streak plate)

Luster: Massive forms are dull or waxy

Fracture: Conchoidal

Cleavage: None - typically breaks with a conchoidal fracture.

Hardness: 7 on Moh's scale

Density/Specific Gravity: 2.6 - 2.7 g/cm3

Magnetism: N/A

Taste: N/A

Hydrochloric acid: N/A

Radioactivity: N/A

Fluorescence: Green fluorescence in short-wave UV light is not uncommon.

Distinguishing Physical Properties:

  • Hardness; (easily scratches glass, also harder than steel)

  • Luster: dull or waxy

  • Fracture: conchoidal

Photograph Attribution: Quartz, variety Microcrystalline, specimen photograph by Sean C. Murphy, 2020.