Organic gemstones
The four organic gemstone groups listed below are highly prized for their beauty and rarity. However, they are not as durable as gemstones from minerals:
Amber (hardness: 2-2.5 Mohs)
A mixture of hydrocarbons
Specific gravity: 1.05-1.096
Hard fossil resin or sap of ancient pine trees. Usually amorphous (lacks crystalline structure). Sometimes mined, sometimes gathered on seashores.
Varies from transparent to semitransparent and generally from light yellow to dark brown, but can be orange, red, whitish, greenish-brown, blue, or violet. Can be dyed in any color.
Takes a fine polish. Used mainly in making beads or other ornaments.
Coral (hardness: 3.5-4 Mohs)
Formed mainly of calcite (calcium carbonate) or conchiolin, a horny organic substance