Gemopedia

Spiny oyster shells are covered with spines and are more closely related to scallops than to oysters. The varieties used in jewelry, are found in the Gulf of California, along the Mexican Pacific coast, the warmer South American waters, and the eastern Mediterranean Sea. It is commonly used in Southwestern jewelry due to its vibrant orange, red, purple, and white colors.

Spodumene is the name of a mineral species that includes two very special gems varieties: kunzite and hiddenite. Spodumene is named from the Greek spodoumenos, meaning "burnt to ash," which alludes to the ashy color of many specimens. A member of the pyroxene group, spodumene belongs to a class of minerals called silicates and it is one of a small number of minerals that contain lithium. Spodumene also occurs in many other shades of colors, all pale but very clear and brilliant. These varieties are given color descriptor names; for example, lemon spodumene.

Stalactites and stalagmites are types of speleothems or cave formations that are formed by slow deposition of minerals by dripping water. These cave formations are formed when rainwater combines with carbon dioxide to create carbonic acid which then permeates carbonate rocks in the subsurface. The acidic water dissolves carbonate material as it filters through the rock. The dissolved carbonate is carried to caves in the subsurface where the carbon dioxide is released and the water evaporates leaving calcite formations to build up over the millennia. Formations hanging from the cave roof are called stalactites while those that build up from the cave floor are called stalagmites. Sometimes the two will join to form a column. Other carbonates such as azurite and malachite, silicates such as opal and chalcedony, limonite, some sulfides, and other minerals can also be deposited. Stalactites are very fragile, and many US states and countries have laws that prohibit collecting them from caves. Some gem material stalactites have been collected as byproducts during mining. Chrysocolla stalactites have been found in the Pearl Handle Pit, in the Ray Mine, Arizona. The Morenci Mine, also in Arizona, has produced goethite and azurite stalactites. Morocco has produced azurmalachite specimens. Large malachite specimens have come from the L'Etoile du Congo Mine, sometimes called the Star of the Congo Mine, in the Democratic Republic of Congo. Vanadinite stalactites have been found in the Mibladen Mining District, Morocco.

George Frederick Kunz originally proposed the name starlite for zircon. The name starlight is sometimes used for blue zircon.

The name staurolite comes from the Greek word stauros, meaning cross. Staurolite is prized for its twinned crystals that intersect at 60- or 90-degree angles forming x-like or perpendicular crosses. Specimens exhibiting these forms are highly prized by collectors. Sometimes referred to respectively as St. Andrew's and Greek crosses, as well as lucky cross, fairy stone or fairy cross, legend says the crystal crosses were created by the tears of fairies who could not help but cry when they heard of Christ's crucifixion. Staurolite is a metamorphic mineral that ranges from translucent to opaque in appearance and facetable gems are very rare.

Stibnite forms as delicate, elongated crystals with metallic luster that are lead-gray in color. It is an important source of antimony. In ancient times it was ground into a powder and mixed with fat to be used as the eye makeup called kohl. It was also a component in ancient flash powder.

Stichtite is purple, purplish pink to purplish red mineral first discovered at Dundas, Tasmania, Australia. It is most often opaque with a pearly or greasy luster. It is most often found in association with serpentine.

Stilbite is named from a Greek term meaning "to glitter" due to the pearly luster of the mineral. A member of the zeolite group, stilbite is often white, peach, pinkish, yellow or brown in color. Stilbite is further classified based on its sodium and calcium content. Stilbite is rarely faceted, but its attractive crystals make it highly collectable as mineral specimens

As its name implies, strontium titanate, also known as Fabulite, is an oxide combination of strontium and titanium. It was originally created as a diamond simulant. Fabulite gems are easy to distinguish from diamonds, as their high dispersion and considerably lower hardness are dead giveaways. For the most part, this jewel fell into obscurity when the hugely popular cubic zirconia (CZ) entered the market in the 1970's. While strontium titanate was originally believed to only be available via laboratory creation, it was discovered in natural form in the 1980's in Siberia and named tausonite in honor of a Russian geochemist.

Sugilite belongs to a class of minerals known as silicates and is a member of the milarite group. A relatively recent addition to the realm of gemstones, sugilite was discovered in 1944 by a Japanese geologist, Ken-ichi Sugi. The mineral is named in his honor. The original find was a yellowish brown variety that was of no interest to the jewelry industry. It was not until 1979 that the first massive aggregates, exhibiting a rich purple color, were discovered in a South African manganese mine. This material was attractive and gained the attention of the gemstone industry. It is predominantly found in the form of cabochons of various shapes and sizes, but has also been used as a component in intarsia jewelry. It is sometimes carved into decorative objects and fashioned into beads.

A gem known since ancient times, sunstone is a type of feldspar formed and crystallized in lava flows. Radiating with the power of eternal light, sunstone has been reportedly found in the tombs of Viking sailors who believed it would aid in their journey through both life and the afterlife. A distinguishing feature of sunstone is its metallic schiller, which rolls across the stone's surface. The effect is due to the presence of small plate-like inclusions of minerals such as hematite or native copper. These inclusions interfere with the passage of light, causing it to scatter. If the inclusions are larger and visible to the eye, they create glittery star-like reflections that gemologists refer to as aventurescence.

Szaibelyite is a basic magnesium borate mineral named after Stephen Szaibely (Sjájbely). It is pale yellow to white and has a fibrous structure.

A rare and beautiful mineral, taaffeite is a lilac to mauve, brown to red, bluish green crystal that may be transparent to translucent in appearance. Interestingly enough, this gem was first discovered as a faceted gemstone that was thought to be spinel. Eventually, the mineral was found in Sri Lanka.

Tahitian pearls, grown around Tahiti and French Polynesia, display a shimmering orient or overtone that is green, blue, pink or violet in color. These orient colors are in striking contrast to their silver to black body color and are sometimes given specific names (e.g., deep green is called fly wing; peacock is used for the combination of green and pink; eggplant is a dark toned body color combined with pink).

Tantalite’s name alludes to the tantalum that makes up a large part of its chemical formula. Tantalite has numerous industrial uses but is only of interest for its mineral specimens and for exotic gemstone collectors. The color ranges from brownish to black sometimes with a red component.

Henry Platt, former president of Tiffany & Co., described tanzanite's discovery in 1967 as the most important gemstone find in 2000 years! A single 5-mile strip of land in Tanzania remains the only commercially viable source of this stone that has become one of the world's most sought-after and admired gems. Tanzanite is a relatively new gemstone in the world of gemology and jewelry. Though its history is brief, it is no less illustrious than many ancient gems. Tanzanite is a single-source gemstone that is a thousand times rarer than diamond, and it is only gaining popularity.

Tektites are unique in that they form when a meteorite melts the surface of the Earth where contact is made. The heat of impact results in molten rock and sand being tossed into the air, raining back down as a natural glass. Tektites are named for the locations where they are found, i.e., moldavite is from the Moldau river area of the Czech Republic. Common colors of this natural glass are yellow, green, gray to black, and colorless.

Teredora™ is a trade name for Triphane or Yellow Spodumene.

Thulite is the translucent to opaque pink variety of zoisite, which is often mottled or streaked with gray or white quartz. The name thulite is derived from its discovery location, Norway, which was once called Thule. This gem is also called rosaline. Thulite is often cut en cabochon for jewelry manufacture or carved into ornaments.

Tiger iron is a rock that is made up of tiger's eye quartz, black hematite and red jasper. These minerals create contrasting bands of color for a truly unique look popularly used for many sorts of ornamentation and decoration.

Tiger's eye is a unique and mysterious member of the quartz family. It ranges in color from rich, golden yellow to bronze and brown. Best seen when gems are cut en cabochon, tiger's eye displays an optical phenomenon known as chatoyancy. Unlike other chatoyant gems, tiger’s eye quartz is made up of quartz with intergrown fibers of amphibole that were altered to golden or rusty-brown limonite. When light hits the surface of this gem, a silky, wavy shimmer moves across the surface of the stone resembling the eye of a tiger. A related variety of quartz called hawk’s eye is blue due to unaltered inclusions of crocidolite.

Titanite gets its name from the titanium in its chemical makeup. Gem quality material is known as sphene. The crystals form as wedge shapes and twinning is common. The color can range from yellow to red, brown, brownish, or yellowish green to green, and black. Specimens can have adamantine luster and high dispersion. Titanite has a high birefringence.

Topaz can be both very common (when clear, or in certain colors like brown, which can turn blue when treated) and very rare (when found in natural beautiful colors rare to the species, like pink and red). Topaz's popularity stems from the gem's good wearability and affordability. Topaz is also often altered with special surface treatments to give it unusual colors and iridescent effects, like mystic, ocean, kiwi, and orchid topaz. Topaz is also a popular birthstone, as blue topaz is December's primary birthstone and yellow topaz is a birthstone for November.

Topazolite is an Andradite Garnet that is yellow or brownish in color. It has a similar appearance to Topaz, and this resemblance inspired its name.