Nephrite is a silicate of calcium, magnesium, and iron, containing fluorine and hydroxyl. It is an amphibole of the actinolite series. It occurs in al...
Obsidian is an extrusive igneous rock, a volcanic glass formed by rapid cooling. Its essential component is glass. Its accessory components are magn...
Oligoclase is a mineral of the plagioclase feldspar series, other members of which are Labradorite and Anorthite. It forms as tabular crystals, whic...
Onyx is a translucent to semitransparent variety of Agate, which in turn is a variety of Chalcedony or cryptocrystalline quartz that is porous and con...
Opal is hydrated silicon dioxide. It has the same chemical composition as quartz but contains about one-tenth (and sometimes as much as one-third) wat...
Orthoclase mineral is a silicate of potassium and aluminum, belonging to the Feldspar group. It has the same composition as microcline, but is stable ...
Padparadschah is the name given to the orange-yellow sapphire, a gem variety of Corundum. It is also differentiated from the yellow sapphire, and is o...
Pearl is one of four main ornamental materials that are classified as "organic" gems, the other three being coral, ivory, and amber. About ...
Peridot is the greener type of gem-quality specimen of Forsterite-Olivine, which is an important, rock-forming mineral, a silicate of magnesium and ir...
Petalite is a lithium aluminum silicate that is an important ore of lithium. This mineral forms, rarely, as small crystals, which are commonly twinne...
