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Rock and Mineral Dictionary
The half-life of a radioisotope is the amount of time it takes for half of the radioisotope to decay.
Halite is a mineral composed of rock salt (NaCl or sodium chloride); it is a crystalline chemical that occurs naturally around the world, in oceans and in salt deposits. The oceans on Earth contain salt (roughly 2.6% salt by weight), as do some lakes. The mineral halite, formed of NaCl, is a colorless to gray to brown crystal. Salt has a hardness of 2.5 and a specific gravity of 2.165. Its index of refraction is 1.5442. NaCl melts at 800.0 °C and boils at 1,465 °C. In solution (dissolved in water), salt is neutral (it is neither acidic nor basic).
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.
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.
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.
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. Rock from Mt. St. Helens is composed of: silicon 60.50%, aluminum 16.60%, iron 6.02%, calcium 5.36%, sodium 4.18%, manganese 2.59%, potassium 1.20%, titanium 0.90%, phosphorus 0.35%, magnesium 0.12%, strontium 0.06%, beryllium 0.04%, copper 0.03%, lead 0.03%, zirconium 0.02%, chromium 0.02%, and zinc 0.02%; the remaining 0.16 percent is sulfur, chlorine, and water.
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 is a synthetic hematite that is made by grinding up hematite, adding a binder (glue) and then press-molding it. The stone is sometimes faceted. Hemalyke looks very much like natural hematite - it is hard to tell them apart.
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. Hematite is found in England, Mexico, Australia, Brazil, and the Lake Superior region of North America.
A hemisphere is half of a sphere.
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 (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.
A hill is a raised area or mound of land.
The Holocene (meaning "entirely recent" in Greek) is the most recent epoch in geologic time, lasting from about 11,000 years ago until the present day (the time since the last Ice Age).
Soil is made up of distinct horizontal layers; these layers are called horizons. They range from rich, organic upper layers (humus and topsoil) to underlying rocky layers ( subsoil, regolith and bedrock).
A hot spot is a an area in the Earth's lithosphere through which magma (molten rock) rises. Volcanoes often erupt over hot spots.
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.
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 (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.
The Hydrologic cycle (also known as the water cycle) is the journey water takes as it circulates from the Earth to the sky and back again.
Rock and Mineral Dictionary
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