Whether it's understanding gemological or jewelry terms in an article you're reading or simply gaining a greater understanding of the world of jewelry and gemstones, our Jewelry & Gem Dictionary is a handy reference guide. And, unlike most dictionaries, ours makes for interesting reading all on its own!

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HALLMARK
A hallmark is an official mark (or a series of marks) made in metal that indicates the fineness of the metal and the manufacturer's mark. For example, a hallmark of 925 indicates 925 parts of gold per 1000 weight. Other hallmarks indicate the maker of the piece and sometimes the year of manufacture. In many countries (like Britain) it is illegal to hallmark metal incorrectly; some countries are notoriously lax in their enforcement of hallmark honesty.

HAMMERED METAL
Hammered metals have been formed, shaped, or decorated by a metalworker's hammer. The surface of hammered metal is covered with crater-like depressions made by a hammer. Many hammered metals are used in jewelry including gold, silver, brass, aluminum, etc.

HARDNESS
A substance's hardness is how resistant it is to being scratched. Hardness is measured using the Mohs Scale of Hardness. In the Mohs scale, one substance is harder than another if it can scratch it. For example, a diamond will scratch garnet, but not the other way around, so a diamond in harder than garnet. This system reliably indicates the relative hardness of gem material and was developed nearly 200 years ago.

• 10 - Diamond (hardest)

• 9 - Corundum

• 8-Topaz

• 7-Quartz

• 6-Feldspar

• 5-Apatite

• 4-Fluorite

• 3-Calcite

• 2-Gypsum

• 1-Talc (softest)

HAWK'S EYE
Hawk's eye is a green, grey or blue variety of quartz that has parallel, fibrous inclusions of crocidolite that give it a greenish cat's eye effect (chatoyancy). This mineral has a silky luster. It looks a lot like Tiger's Eye, and often occurs with it in the same rock, but the internal structure is different.

HEAD
the part of the setting that holds the center stone or solitaire in place.

HEAD SHAPE
The shape of the head, which is determined by the shape of the gemstone the head holds. For example, the head that holds an ideal-cut diamond is round, whereas a head that holds a princess-cut diamond is square.

HEAD-SIZE RANGE
The range of carat weights of gemstones that can be mounted into a particular head.

HEAT TREATMENT
Heat treatment is the heating of stones to a high temperature in order to enhance the color or clarity. For example, blue-green aquamarine becomes blue with heat treatment and brown zircon becomes blue or clear. chromium .02%, and zinc .02%; the remaining 0.16 percent is sulfur, chlorine, and water.

HEISHI
Heishi (pronounced he-she) is jewelry made from disk-shaped beads of shell (or turquoise, lapis lazuli, and other stones). Each bead begins as a tiny flat piece of shell (or stone). A tiny stringing hole is drilled though the fragment. Many of these jagged pieces are strung together tightly on a wire and are then sanded into evenness using a fine-grained sandstone and then sandpaper. The result is a very smooth strand of disk-shaped beads. This is an ancient form of bead-making developed by the Pueblos of North America.

HELENITE
Helenite is a manmade (not natural) green glass that is made from "rock dust" (not volcanic ash) taken from the vicinity of the Mt. St. Helens volcano in Washington state. The dust is fired to 2700 degrees F, forming glass, which is later faceted and used as a gemstone. This glass is sometimes called emerald obsidianite or Mount St. Helens obsidian (but it is not obsidian, which is a natural glass). Helenite is sold as a souvenir of the eruption of Mt. St. Helens on May 18, 1980. The composition of rock from Mt. St. Helens is: Rock from Mt. St. Helens is composed of: silicone 60.50%, aluminum 16.60%, iron 6.02%, calcium 5.36%, sodium 4.18%, manganese 2.59%, potassium 1.20%, titanium .90%, phosphorus .35%, magnesium .12%, strontium .06%, Beryllium .04%, copper .03%, lead .03%, zirconium .02%, chromium .02%, and zinc .02%; the remaining 0.16 percent is sulfur, chlorine, and water.

HELIOTROPE
Heliotrope (commonly known as bloodstone) is an inexpensive type of chalcedony that is green with red highlights (caused by iron oxide). Heliotrope is porous and relatively soft.

HEMALYKE
Hemalyke is a synthetic hematite that is made by grinding up hematite, adding a biner (glue) and then press-molding it. The stone is sometimes faceted. Hemalyke looks very much like natural hematite - it is hard to them apart.

HEMATITE
Hematite (sometimes spelled haematite, and also known as kidney ore) is a lustrous, opaque, blue-black to silvery gray mineral often used in jewelry. Hematite is iron oxide (Fe2O3). Hematite has a hardness of 6.5 and a specific gravity of 4.95 to 5.16. When powdered, hematite is red; when rubbed on a hard stone, it leaves a red streak. Hematite was often used as seal stones, cut as intaglio. It is also used as beads and is faceted, carved or cut as a cabochon for use as a gemstone. The ancient Egyptians carved hematite into scarabs. Hematite is found in England, Mexico, Australia, Brazil, and the Lake Superior region of North America.

HERKIMER DIAMOND
Herkimer diamonds are clear, lustrous, doubly terminated crystals of quartz - they are not true diamonds. These brilliant stones are also called "Middleville Diamonds" or "Little Falls Diamonds." Herkimer diamonds have a hardness of 7. This stone is found in Middleville and Little Falls, Herkimer County, New York, USA.

HESSONITE
Hessonite (also called "cinnamon stone") is a cinnamon-brown to orange gemstone variety of grossular garnet. Hessonite's formula is Ca3Al2Si3O12; manganese that gives it its characteristic brown color. This transparent stone has a hardness of 6.5 - 7 and a specific gravity of 3.6. Hessonite is found in Sri Lanka, Brazil, Madagascar, Canada, and California, USA. This stone is not enhanced

HOOK AND EYE CLASP
A hook and eye clasp is a simple and ancient jewelry fastener that is composed of a hook and a circular piece that the hook can latch onto. It is used to attach the two ends of a necklace or bracelet.

HOWLITE
Howlite is a soft, white to gray mineral that takes dye very easily, and can be dyed to imitate turquoise very well (and is sometimes unscrupulously sold as turquoise). Howlite was named for its discoverer, Henry How, a Nova Scotia geologist.

HUE
A term used to describe the attributes of a gemstone's color.

HYACINTH
Hyacinth is a semi-precious stone that is also known as jacinth. it is a lustrous orange-yellow, orange-red, or yellow-brown type of zircon. Hyacinth has a hardness of 7.5 and a specific gravity of 4.65. Sometimes, topaz and grossular garnet of this color are also referred to as hyacinth (this can be very confusing). Hyacinth is mined in Sri Lanka. Even more confusing is the origin of the name, which comes from the Greek hyakinthos, which refers to blue gemstone.

HYACINTH OPAL
Hyacinth opal (also known as girasol) is a yellow or orange type of precious opal. In this opal, the play of colors seems to come from within the stone, like a floating light, and seems to follow the light source.

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