calcite - cool pink fluorescent and phosphorescent calcite - cleavage rhomb from the Challenger Cave system, Nuevo Leon, Mexico with its natural purplish oxidized

with its natural purplish oxidized surface

sometimes with a hollow center

The Navajo sandstone is widely  exposed in southern Utah and forms the colorful crossbedded cliffs at Zion National Park

Locally it is poorly to moderately well cemented with silica cement

This medium-grained sandstone is composed primarily of quartz with feldspar and some biotite

calcite - cool pink fluorescent and phosphorescent calcite - cleavage rhomb from the Challenger Cave system, Nuevo Leon, Mexico with its natural purplish oxidizedCalcite, CaCO3, is an extremely common rock forming mineral. In pegmatites it forms large masses and it makes up some limestones almost entirely. It has a large variety of crystal forms, but these do not include the rhombus shaped pieces that are sold as calcite crystals. The rhombs are produced by cleaving calcite in three directions between rows of atoms. When calcite is free of impurities and is optically clear, it exhibits double refraction. When