Welcome to the Mineral and precious stone glossary
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Gem without facets that is highly polished and has smooth, rounded edges.
Containing the compound calcium carbonate.
Containing calcium.
Group of minerals belonging to the carbonate group that are isomorphous with one another and have the same properties, such as that they all:
Gem with a design or figure carved out of the stone, and raised above the background layer.
Aggregate composed of tiny, thin, straight, long crystal strands; hairlike. (i.e.Millerite)
Weight measurement used in reference to gemstones in regard to their evaluation. A carat is .2 grams (or 200 milligrams), and this weight is used worldwide, even in the U.S. where the metric system isn't used. A point is the weight used only in reference to very small, precious gemstones, and represents 1/100th of a carat. The abbreviation for carat is Ct. and for point is Pt. The term carat in regard to gemstones should not be confused with the term carat in regard to gold. By gold, it refers to the content of gold a gold ornament contains. Because of the confusion, the term carat in regard to gold has been changed to karat. (See karat)
Group of minerals that contain one or more metallic elements plus the carbonate radical (CO3). Most are lightly colored and transparent when pure. All carbonates are soft, brittle, and effervesce when exposed to warm hydrochloric acid.
The carbonates are divided as follows:
Calcite Group
Aragonite Group
The Nitrates and Borates are sometimes considered a category of the carbonates.
Form of penetration twinning where two Orthoclase crystals form interpenetrating twins
Ornamental figure, such as a stone lion, carved out of a rock or mineral.
Neutral atom that loses an electron and becomes positively charged.
A mineral with dense inclusions of tiny, parallel, slender, fibers that may cause it to exhibit chatoyancy. The most notable cat's eye mineral is Chrysoberyl Cat's Eye, which is known simply as Cat's Eye. Other cat's eye minerals are termed by their respective names, such as a cat's eye Quartz is known as "Quartz Cat's Eye".
Large hollow cavity in the earth surrounded by a carbonate or sulfate composed material (usually Calcite) that has an opening to the surface. Caves develop through underground streams carving out the underground minerals.
Hollow area in rock that develops because of some form of stress. Many cavities are lined with crystals. (See vug)
Underground area where certain elements are concentrated and can combine to form new, or primary, minerals.
Central area on a polyhedron where all the planes of symmetry intersect.
Phenomenon of certain cat's eye minerals which causes it to exhibit a concentrated narrow band of reflected light across the center of the mineral. Chatoyancy is usually only seen on polished cabochons.
A substance with a distinct molecular formation, produced by a chemical process.
A force by which atoms are bound in a molecule or crystal.
The scientific method of describing what elements a material is composed of. See The Chemical Properties of Minerals for more information.
The study and science of the composition and structure of all substances.
Individual practicing in the subject of chemistry.
Group of minerals that are compounds of one or more metallic elements combined with the chromate radical (CrO4). Minerals in this group are usually brightly colored and heavy. The chromates are rare minerals and are usually classified as a sub-group of the sulfates.
Form of contact twinning, in which six Chrysoberyl crystals join at the base, forming a six-pointed formation
Fragment of rock or mineral broken off from a large piece.
A mixture of very fine grains of micaceous substances. Clay is plastic when wet and hardens when heated. It consists mainly of hydrous aluminum silicates.
The splitting or tendency of a crystal to split along definite crystalline planes to produce smooth surfaces. (See Cleavage in mineral properties for more information.)
Crystallized fragment that broke off of a mineral that exhibits cleavage.
Broken surface of a mineral that has a flat surface where the mineral broke, proving that the mineral exhibits cleavage.
Dense agglomeration of crystals.
Black, staining, greasy, rock formed by the accumulation of herbal organic matter, such as leaves and grass.
A thin layer of one mineral on the surface of another.
The characteristic color or colors of a mineral. (See Color in mineral properties)
Aggregate defining a mineral which has parallel, slender, compact, adjoining crystals.
The elements and the quantity of the elements a substance contains.
An association of two or more elements that can only be separated by chemical means.
Aggregate describing foliated masses that are somewhat spherical and rotate about a center; appearing like a rose (rosette). Also used to describe a form of banding where the bands are circular, forming rings about a central point.
Mineral fracture in which the indentation resembles a shell. (See Fracture in mineral properties for more information.)
Aggregate composed of a mass of small crystals that become cemented together, resulting in a rounded, odd form.
The ability to conduct electricity.
1) A substance capable of transmitting electricity, such as a metal.
2) Something that is able to retain a substance such as heat or pressure.
The process of mineral or rock metamorphism which is caused from magma intrusion near the contact with the magma.
Form of twinning where two crystals join together at a base. Examples: japanese twin, spinel twin, and chrysoberyl twin.
Fossilized animal excrement embedded in rock.
Marine polyp that secretes calcareous skeletons. The skeleton is also called coral, and is used as an ornamental stone.
The innermost layer of the earth, containing its center.
Aggregate composed of flaky or tabular crystals that seem adjoined from a base; with grooves between long, slender, arc-like crystals. (i.e. Barite)
A hole that was created in the earth or celestial body from the impact of a meteor.
Condition in Opal that causes it to form small, internal cracks, and in some severe cases will eventually disintegrate the Opal.
A disorganized, crusty, mineral coating that can be thin or thick. Type of aggregate.
Aggregate of a crust coating on a rock or mineral.
Composed of tiny, microscopic crystals. See also microcrystalline.
Any particular three dimensional form a mineral exhibits; which is classified by the distance ratio and angle of constituent parts. (See Crystals in Mineral Properties for more information.)
The sum of the angles on a crystal edge that are characteristic to a crystal set. (See Crystals in Mineral Properties for more information.)
The method of classification used to classify the 32 different crystal types. The distinctions between the different crystal types is based on their symmetry. Crystal class in not to be confused with "crystal system" or "crystal group", which are the primary crystal classification categories. (See Crystals in Mineral Properties for more information.)
The habitual form that a mineral forms its crystals as. (See Crystal Habits in mineral properties for more information.)
The arrangement of atoms in a crystal, giving each crystal its distinct shape. See also crystal structure.
The framework of a crystal, usually referring to its molecular arrangement.
The primary method of classification of crystals. The Crystal system classifies crystals in six groups. They are: Isometric, Tetragonal, Hexagonal (which includes Trigonal), Orthorhombic, Monoclinic, and Triclinic. The crystal class, which classifies crystals into 32 crystal types, is a more precise classification of crystal groupings. (See Crystals in Mineral Properties for more information.)
1) Having a crystal structure.
2) Composed of visible crystals
The forming of crystals or to assume a crystal shape.
To form a crystal shape, or to have crystals in a particular group (i.e. Diamond crystallizes in the isometric system).
Type of cleavage exhibited on minerals of the isometric system that are crystallized as cubes. The method of cleavage is that small cubes break off of an existing cube. Example = Galena.
Group of silicate minerals that have their tetrahedrons linked into rings. Each silicon atom is bound by two oxygen atoms that are part of another tetrahedron. Each ring consists of three, four, or six linked tetrahedrons. For more information, see "All About the Silicates Group".
Phenomenon seen on a few polished gems that cause it to exhibit a floating light reflection that moves as the gem is rotated