fuchsite a glassy, deep green variety of muscovite.
garnet a group of minerals, the most popular of which is pyrope. Often, a red, semiprecious crystal resembling a pomegranate seed, but garnets come in all colors except blue.
gastrolith any stone ingested by an animal to aid in digestion.
geode a globular rock with a cavity lined with minerals.
glacial pavement rock paved over by glaciers, leaving telltale scrapes, scars, and gouges, or a polished appearance.
gneiss a common metamorphic rock similar to granite.
granite a hard igneous rock composed of quartz, feldspar, and mica; a popular building material.
greenstone an alternate name for nephrite, a variety of jade.
heliotrope see bloodstone.
herkimer diamonds a clear form of crystal quartz, not an actual diamond.
hornblende a green or black mineral, found in igneous rock, and one of the components of granite.
humus the dark, organic matter found in soil.
hyacinth opal a yellow or orange form of opal. Also known as girasol.
igneous rock a class of rocks formed from cooled magma or lava.
imperial jade an emerald-green form of jade.
imperial topaz a very valuable form of orange- yellow topaz.
intrusive of or relating to igneous rock or magma that forces its way into or between other rocks and solidifies before reaching the Earth's surface.
ironstone a heavy, sedimentary rock with a high iron content.
jacinth a red, translucent zircon used as a gemstone.
jade a very hard stone, composed of two different minerals, jadeite and nephrite, and highly prized for its beauty. Although it comes in different colors, the green variety is most sought after, especially for jewelry.
jasper an opaque quartz that may be red, yellow, brown, or green, with swirls and bands of colors.
karst a topography of limestone characterized by numerous sinkholes or caverns.
lapidary one who cuts and polishes gemstones.
lapilli small volcanic fragments from pebble to cobble size.
lapis lazuli a semiprecious stone characterized by its royal blue color interspersed with gold flakes of pyrite and white streaks of calcite.
limestone a sedimentary rock composed of calcium carbonate from deposits of various marine creatures.
lithification the process of rock formation.
loess deposits of windblown silt.
mabble a metamorphic rock, often white and swirled with various colors.
malachite an opaque, semiprecious stone, usually greenish because of its high copper content.
marble metamorphosed limestone.
marbled having swirls of colors, like marble.
matrix the natural rock in which a gemstone is embedded.
melanite a black garnet.
metamorphic rock rock that has been "metamorphosed" or altered by heat, steam, or pressure to form other types of rocks.
Mexican diamond not an actual diamond but rock crystal.
mica a soft, transparent mineral that forms in sheets that can be peeled or flaked off, and which can appear in various colors.
Mohs scale a scale, from 1 to 10, designating in gemstones the degree of their hardness and resistance to scratches, with diamonds being the hardest of all and rated a 10. A diamond can scratch all other gems, but it cannot itself be scratched.
moldavite a rare green and glassy gemstone formed by meteorite impacts.
moonstone a variety of feldspar, characterized by a milky, bluish luster. See adularescence.
morganite a brittle, translucent pink gemstone, a member of the beryl family.
moss agate a green agate with dendrites of green, red, or black.
nanodiamonds also known as microdiamonds, tiny diamonds created by the impact of a meteorite on Earth.
nephrite a semiprecious variety of jade, often used to make vases and carvings.
nugget a lump of precious metal, such as gold.
obsidian a lustrous black volcanic glass found in lava flows and occasionally found in other colors.
oil shale a shale rich in organic material, suitable for energy conversion.
onyx a variety of agate, found in pure black but more often banded in black and white and a variety of other colors. Often cut into cabochons, cameos, and beads.
oolite a tiny round grain or pellet made of calcium carbonate or quartz found in limestones and dolomites.
opal an iridescent, semiprecious stone, usually having numerous inclusions that create rainbowlike reflections.
ore any earth material from which useful commodities can be extracted.
outcrop a jutting out or other natural exposure of bedrock.
overburden loose rock material lying on top of bedrock.
peacock pearl a very dark, naturally formed green pearl.
Pearl of Allah also known as the Pearl of Lao Tzu, the largest pearl ever found, weighing in at 14 pounds (6.4 kg), and actually taken from a giant clam.
pegmatite a coarse igneous rock composed of multiple elements, including feldspar, mica, and quartz, which may also be found with aquamarine, topaz, or tourmaline.
Pele's hair threadlike strands of volcanic glass.
peridot a variety of olivine, an olive-green gem found in lava flows and in meteorites, sometimes mistaken for emerald.
petrify to turn wood or any other organic material into stone by the intrusion of dissolved minerals.
petroglyph a line drawing or carving on a rock face.
petrology the study of rocks and minerals.
petrous pertaining to or resembling a rock.
placer deposit an alluvial or glacial deposit of sand and gravel that contains valuable minerals.
pumice a volcanic rock of a "frothy" appearance, often light enough to float on water.
pyroclastic containing consolidated volcanic fragments.
pyrope a form of garnet, characterized by its blood- red color, and sometimes misleadingly sold as a ruby under the names American ruby, Bohemian ruby, California ruby, Cape ruby, Montana ruby, and Rocky Mountain ruby.
quartz a crystalline mineral found in various forms and colors and includes amethyst, aventurine, citrine, opal, and others.
quinzite opal a red or pink opal.
rimrock on the edge of a plateau, the topmost layer of sheer wall.
riprap a layer of broken stones applied to an embankment of a river, lake, or ocean to help prevent erosion.
rose quartz a pink to red quartz. rubellite a red tourmaline.
ruby a precious stone found in pink, red, purple, and brown and rated second in hardness to diamonds.
rutilated quartz a crystal containing needles of titanium dioxide, which create asterisms, and usually cut into a cabochon. Also known as Venus's hair stone and Cupid's darts.
rutile a needlelike inclusion found in some gem- stones, creating asterisms or other effects.
sandstone rock made of sand grains bonded together.