amethyst - crystal clusters - set of five student specimens from Brazil " and rhein

" and rhein

but they are decent student specimens at a decent price

Occasionally the metamorphism produces a pegmatite with large crystals that form when a fluid-rich magma allows rapid movement of atoms

Much of this reaction to ultraviolet is directional - illuminate a rhomb from one direction and the reaction is strong

The sand grains are entirely frosted quartz

amethyst - crystal clusters - set of five student specimens from Brazil " and rheinAmethyst quartz SiO2 These amethyst crystal clusters formed as linings in gas bubbles in the Parana flood basalts in Rio Grande do Sul province, Brazil. Recent 40Ar 39Ar dating shows these basalts erupted over a roughly 2 million year period beginning 135 1 million years ago. The Parana Etendeka flood basalts cover an extensive area in southern Brazil and parts of Uruguay, Paraguay and Argentina in South America and in Namibia and Angola in