Calcite on Amethyst Geode
Image: <bdi><a href="https://www.wikidata.org/wiki/Q56247090" class="extiw" title="d:Q56247090"><span title="mineral collector and dealer">Robert M. Lavinsky</span></a></bdi> (CC BY-SA 3.0)
Mineral NameCalcite on Amethyst Geode
Chemical FormulaCaCO3 (Calcite), SiO2 (Amethyst)
Mohs Hardness3 (Calcite), 7 (Amethyst)
Lustervitreous
Streak ColorWhite
CleavagePerfect rhombohedral in 3 directions (Calcite); None (Amethyst)
FractureConchoidal (Amethyst), Conchoidal to uneven (Calcite)
Specific Gravity2.71 (Calcite), 2.65 (Amethyst)
Colorspurple, white, cream, grey
TransparencyTransparent to translucent
Type LocalityIdar-Oberstein, Hunsrück Mts, Rhineland-Palatinate, Germany
Mineral GroupCarbonates (Calcite),Silicates (Amethyst)
Usescollector specimens, jewelry (amethyst)
Associated Mineralsquartz, amethyst, calcite
Rarityuncommon
Description
This specimen is a geode fragment featuring a cavity lined with small, vibrant purple amethyst crystals, upon which larger, blocky to tabular white and cream-colored calcite crystals have grown.
Geological Context
This geode formed within volcanic rocks, likely basalt, where silica-rich solutions deposited amethyst quartz in a cavity. Later, calcium-rich hydrothermal fluids precipitated the calcite crystals within the same void.
