Herkimer diamonds, the special double-ended stones from upstate New York.

Amethyst owes its color to the presence of iron atoms in the crystal matrix, which otherwise consists of silicon and oxygen in the proportion SiO2. ...

Amethyst specimen showing typical shapes of quartz crystals.

Pure, clear quartz is called rock crystal. Crystals always show a ... But in pegmatites quartz can sometimes form very large crystals, as long as a meter. ...

A well-formed crystal of grossular garnet, from Michoacan, Mexico. ... The garnets usually form good crystals with this form—round with 12 sides ...

A whole zircon crystal, slightly twinned, in loving closeup. ... Zircon always occurs in crystals like this 8-millimeter twinned specimen from Mexico, ...

A natural diamond grain from Congo shows rough crystal faces. ... Diamonds occur in a range of forms, from nearly perfect crystals to rough grains like this ...

When it forms true crystals, calcite takes platy or spiky shapes. ... The offset is due to refraction of the light traveling through the crystal, ...

This Chinese tourmaline specimen, shown about twice life size, displays the typical crystal shape of a nine-sided prism. It also displays the typical ...

Fluorite also occurs in several different crystal forms. ... Usually fluorite crystals are cubic, like halite, but they can also be octahedral and other ...