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, alumimum, 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.

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.

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.

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.