Mary Ellen is a rock that consists of red jasper and silvery hematite. The jasper is a fossil stromatolite, a layered structure built up by sediment-trapping algae that lived on Earth about two billion years ago - long before land plants.
Matrix opal is a material in which precious opal is in an intimate mixture with the host rock, instead of being confined to seams and patches.
Maw sit sit is a rock composed of jadeite, albite, and kosmochlor (a mineral related to jadeite). It is attractive, has a bright chrome-green color and accepts a bright polish, and for those reasons it is used as a gemstone.
Melanite is a lustrous, black, opaque variety of garnet that is not often seen in jewelry. It is a titanium garnet of the Andradite group and is sometimes called "titanian andradite."
Moldavite is a glassy material that is thought to have formed when a large asteroid impacted a location in Europe about 15 million years ago. The target rock and impactor melted and solidified into an olive green glass.
A colorful gem material mined in Australia that forms from the deposition and lithification of a sediment composed of the silica tests of radiolarians. It is a popular material for cabochons and beads.
Moonstone is a name given to translucent orthoclase feldspar that exhibits adularescence (a white-to-bluish light that floats under the surface of the stone when it is turned under a source of light).
Morganite, also called "pink beryl," is the pink- to salmon-colored gemstone member of the beryl mineral group.
Moss agate is a transparent-to-translucent chalcedony that contains mineral inclusions that are shaped like moss, trees, leaves, or other vegetation. Material from Montana localities is very popular.
Mother of pearl, also known as "MOP," is the thin inner nacreous layer of a mollusk shell. It can be white, cream, or gray in color with a beautiful iridescent play-of-color. Used in jewelry, buttons, musical instruments, and more.
Nephrite and jadeite are two very similar minerals that are both known as "jade." Nephrite is the more abundant and less valuable mineral of the pair - but it can still have great beauty and appeal.
A gem material named because it is found below the high tide line of a Madagascar ocean beach. It is patterned with beautiful eyes and bands in a wide variety of colors. It also can grade from agate to jasper in a single stone.
Onyx is the name given to a black chalcedony with parallel white banding or a red chalcedony with white banding. High-quality pieces are sometimes used to carve cameos.
A spectacular gemstone that produces flashes of iridescent color when moved under incident light. Opal also occurs as nonphenomenal gems with beautiful body color. There are many types of opal.
A type of petrified wood that is composed of opal, usually common opal, rather than chalcedony or another mineral material.
A variety of petrified wood from Australia. Some pieces have white markings that remind people of peanuts. It is a fossil driftwood that has been bored by marine clams.
Pearls are a very popular gem material. They are produced by shellfish, and people have used them for personal adornment for thousands of years. These are cultured freshwater pearls produced in Tennessee.
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Peridot is a popular green gemstone from the olivine mineral series. It is widely used in commercial jewelry and is a birthstone for the month of August.
Louisiana has been the "bayou state" for over 100 million years. During that history, many palms have been fossilized. Today they are called "petrified palm wood" (but they really are not wood) and polished into beautiful gems.
A fossil that is formed when woody material is buried, then dissolved materials in groundwater precipitate to replace and infill the wood structure with silica, opal, or other mineral material.
An opal that exhibits pin points of fire instead of a broad flash is known as "pinfire opal." There are many types of opal.
Pinolith is a metamorphic rock composed of white magnesite crystals on a background of graphite-pigmented dolomite. It is a rare material that is found only in Austria and Spain.
A beautiful blue to white to yellow translucent agate with lots of colorful dots. It is an American gemstone mined in Oregon.
Prasiolite is amethyst that has been heat-treated to a leek-green color.
Prehnite is a calcium aluminum silicate mineral. Specimens with nice color and clarity are often cut as gems. This gemmy yellow prehnite cabochon was cut from material mined in Australia.
Purpurite is a manganese phosphate mineral with a bold purple color that is often cut into cabochons. It has a low hardness (4 to 5) so is best used in jewelry that is not expected to receive rough wear.
Pyrope is a magnesium aluminum garnet that is usually red in color. It is often formed in the mantle and transported to the surface in deep-source volcanic eruptions that form diamond deposits.
Quartz is the most common mineral in Earth's crust and often occurs in colored gem-quality crystals. These include rose quartz, amethyst, smoky quartz, citrine, lemon quartz, and others.
Clear quartz is a common mineral material that is sometimes cut as a gem. It is often called "crystal quartz" or "rock crystal." It is the state mineral of Arkansas.
Rare specimens of clear quartz have needle-shaped inclusions of rutile. These can be used to cut interesting and attractive cabochons and faceted stones.
Rare specimens of clear quartz have needle-shaped inclusions of tourmaline. These can be used to cut interesting and attractive cabochons and faceted stones.
Rainbow moonstone is a variety of moonstone that displays an electric blue or multicolor adularescence within a stone of colorless or white bodycolor.
Red beryl is an extremely rare gemstone colored by trace amounts of manganese. It is produced at one location in the world, the Ruby-Violet claims in Beaver County, Utah.
Rhodolite is a purplish red to violet-red variety of garnet that is a combination of pyrope and almandine. It often has wonderful color and clarity at a relatively low cost - and that is helping it become popular in jewelry.
Rhodochrosite is a manganese carbonate mineral that is popular because of its beautiful pink color. It typically has lacy or concentric bands. Its softness limits its use to earrings, pendants, pins, and other low-abrasion items.
Rhodonite is a manganese mineral that sometimes occurs in a very attractive pink color. Usually translucent to opaque, it is a popular gem material. Rarely, it is transparent and used for faceting.
Rose quartz is a translucent-to-transparent variety of quartz with a light to deep pink color. It is a gem material that is very common in nature. It is usually cut into cabs and occasionally faceted.
Ruby is the most popular colored stone. When the mineral known as corundum is of gem quality and a vivid red color, it is called "ruby." Historically mined in Asia, many rubies such as these are now being found in Africa.
Fuchsite is a metamorphic mica with a green color that often contains bright red corundum crystals or "rubies." It is often carved and cut into cabochons. Frequently confused with "ruby in zoisite."
Ruby in zoisite is an interesting material. Massive green zoisite often contains bright red ruby crystals. The color combination makes an attractive and unique gem material. It is often cut and carved into small sculptures.
Sand dollars found on beaches today are remains of a group of animals that has lived in the oceans for millions of years. Their bodies are often agatized by nature and then found by people who polish them into gems.
Sapphire is a gem variety of the mineral corundum. When it is reddish blue to violet-blue, it is known simply as "sapphire." Corundums of any other color (except red, which is ruby) are known as "fancy sapphires."
Star sapphire contains elongated crystals of rutile aligned in three different directions that cause a properly cut stone to display a six-ray star. This phenomenon is known as "asterism."
Sardonyx is a member of the chalcedony family. It is a banded agate that contains bands of bright red alternating with agate of other colors.
Scapolite is a metamorphic mineral that sometimes occurs in transparent gem-quality crystals that make beautiful faceted gems. Some specimens contain a silk that can produce a strong cat's-eye.
Cat's-eye scapolite contains a silk of parallel mineral fibers. When cut as a cabochon, the silk reflects light to produce an "eye" that moves across the stone.
"Septarian" is a name used for round concretions with internal mineral-filled fractures found in sedimentary rocks. They are often cut into cabochons that display the interesting geometry of the fracture network.
Seraphinite is a trade name used for a gem material composed of the mineral clinochlore. It is usually greenish in color and marked with fibrous or feather-like patterns. Its hardness is only 3 to 4 and is reserved for delicate use.
A silicate mineral that occurs in a wide range of green and greenish colors with interesting patterns. Serpentine is often cut into cabochons or used as an ornamental stone.
Siderite is an iron carbonate mineral with a very high dispersion. Transparent crystals of siderite with great clarity can be cut into attractive gemstones with a strong fire. It is too soft for most jewelry and is a collector's stone.
Sillimanite is a metamorphic mineral that often has a fine fibrous silk. When properly cut, cabochons of the material can reflect a sharp cat's-eye.
Silver is a precious metal that is often present as visible crystals in its ore. Some people enjoy seeing the bright metal reflecting from the surface of a cabochon. It is a novelty gem.
Smithsonite is a zinc carbonate mineral that serves as a minor ore of zinc and as a minor gem mineral. It is relatively soft and used as a collector's gem and in jewelry that is unlikely to receive abrasion or impact.
Smoky quartz is a grayish brown to nearly black variety of transparent quartz. It is often cut as a faceted stone or cabochon. Upon heating, it will sometimes change in color to yellow or yellowish brown citrine.
A feldspathoid mineral that ranges in color from white to blue to violet blue. It is often used to make cabochons, tumbled stones, and other lapidary projects.
Sonora Sunrise is a trade name for an eye-catching red and green gem material. It occurs naturally as a rock composed mainly of bluish-green chrysocolla and bright red cuprite.
Some specimens of gem-quality labradorite have exceptional color and labradorescence. These unusual gems are given the name "spectrolite" because of the spectrum of colors that they reflect.
Spessartine is also known as "spessartite" or as "mandarin garnet" because of its yellow-orange to orange-red color. It is a popular variety of garnet used in jewelry.
With a dispersion that is 3x that of diamond, sphalerite can be a very attractive faceted stone. It is popular with collectors but has very limited jewelry use because of its very low hardness (3.5 to 4) and perfect cleavage.
Sphene, also known as titanite, is a gem with a dispersion higher than diamond. Specimens of high clarity can be cut into gems with a brilliant fire. Its softness limits its use to earrings, pins, pendants, and low-abrasion jewelry pieces.
A trade name for pink to red quartz that obtains its color from tiny red inclusions. This novelty gem received its named because the inclusions often look like strawberry seeds!
A mineral of many colors that has been treasured as a gem for thousands of years. It was often confused with ruby and sapphire. Many of these errors were not discovered until the 20th century.
Sugilite is a rare silicate mineral only discovered in 1944. It occurs in yellow, brown, pink, and purple and is often combined with quartz. The purple color has become very popular in the lapidary trade. Its high price limits its popularity.
A plagioclase feldspar that can be a colorful transparent gem. It can also contain plate-shaped copper inclusions that produce an aventurescent flash when moved under incident light. These specimens are from Oregon.
Tanzanite is a rare and popular blue variety of zoisite produced from a small location in the African country of Tanzania. It is a birthstone for the month of December and is an alternative stone for blue sapphire.
Tektites are fragments of ejecta produced when an asteroid struck Earth about 800,000 years ago. The impact melted the target rock and scattered a black glass in a strewn field across southeastern Asia.
Thulite is a rare, pink, gem-quality variety of zoisite. It can be cut into beautiful cabochons, beads, small sculptures, and other lapidary items.
Tiger's-eye is a material that forms when quartz replaces crocidolite. When it is cut into a cabochon with its fibrous structure parallel to the bottom of the stone, a chatoyance, or cat's-eye effect, is produced.
Tiger iron is a rock composed of alternating bands of silver hematite, gold tiger's-eye, and red jasper. It is cut into attractive and interesting cabochons, beads, spheres, and other lapidary items.
Also known as "bertrandite," Tiffany stone is a beautiful material that is thought to be an opalized fluorite. Found at one beryllium mine site in Utah.
Topaz is a popular gem. It is usually clear to amber in color when mined. It can be heated, coated, or irradiated to produce other colors that include "Swiss blue," "London blue," bright pink, and soft pink.
Tourmaline is a silicate mineral that occurs in a wide range of attractive colors. It is a very durable gem material that is popular with jewelry makers.
Color-zoned crystals of tourmaline that have two zones of contrasting color. The favorite is "watermelon tourmaline" because of its pink and green zoning. :-)
Tsavorite is a calcium-rich garnet known for its brilliant green color. It sometimes serves as an alternative stone to emerald. It is the most important green garnet and one of the rarest and most valuable colored stones.
A copper mineral with a bright blue to blue-green color. The color is so familiar and liked that the word "turquoise" is used in the English language as the name of a color. Only a few gems have a color this familiar.
Decades ago, this agate was named "Turritella" after the fossil snails that it contains. That name is incorrect because the snails were misidentified. The proper name should be "Elimia agate" after the snail Elimia tenera.
Unakite is an igneous rock that contains green epidote and pink orthoclase feldspar. It can be coarse or fine grained. It is popular as cabochons, beads, and small sculptures.
A mineral that is similar to turquoise in mode of formation and composition. It even looks like turquoise but in a blue-green to yellowish green color. Cut into cabochons, but its use is limited because it is soft (H: 4.5).
Vesuvianite is a mineral formed by the contact metamorphism of limestone. It is often an attractive translucent green color that reminds people of jade. Rare transparent crystals are faceted. Named after Mt. Vesuvius.
"Light opal" or "white opal" are terms used for an opal material with a white, yellow, or cream-colored body color. This is the most common body color for precious opal. There are many types of opal.
Zircon is a hard, durable gem that occurs in a variety of colors. Its brightness and fire rivals those of diamond. Colorless zircon was once used as a popular and fraudulent alternative to diamond.
We highly recommend Gemstones of the World by Walter Schumann. It is one of the most popular gemstone books ever written - over one million copies sold. It has about 100 pages of basic gem information and about 200 pages dedicated to photos and descriptions of over 100 gems and gem materials. A well-illustrated book for the beginner and contains essential reference material for anyone interested in gems.
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