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Inland Lapidary - Gem glossary
Category: General technical and industrial > Gems and Geology
Date & country: 27/10/2013, USA
Words: 1119


glacier
A moving body of ice that forms on land from the accumulation and compaction of snow, and that flows downslope or outward due to gravity and the pressure of its own weight.

glassy (luster)
Synonym of vitreous luster.

glauber's salt
Salt made of sodium sulfate (Na2 SO4 �10H2O) used in the manufacture of paper and glass and in stomach medications. Glauber's salt is extracted from the mineral Glauberite

globular
The term globular is used as a synonym of botryoidal, but sometimes describes any rounded agglomeration, such as botryoidal, reniform and mammilary.

gneiss
A coarse-grained, foliated metamorphic rock marked by bands of light-colored minerals such as quartz and feldspar that alternate with bands of dark-colored minerals. This alternation develops through metamorphic differentiation.

goniometer
Instrument that measures crystal angles.

graben
A block of rock that lies between two faults and has moved downward to form a depression between the two adjacent fault blocks. See also horst.

graded bed
A bed formed by the deposition of sediment in relatively still water, marked by the presence of particles that vary in size, density, and shape. The particles settle in a gradual slope with the coarsest particles at the bottom and the finest at the top.

graded stream
A stream maintaining an equilibrium between the processes of erosion and deposition, and therefore between aggradation and degradation.

gradient
The vertical drop in a stream's elevation over a given horizontal distance, expressed as an angle.

grain
1. Individual component belonging to a grainy aggregate. 2. Weight used in reference to measuring pearls. A grain is .05 grams or � carat.

grainy
Crystal aggregate resembling a cluster of grain.

gram
Weight measurement used to measure less valuable gems or rough stones. It corresponds to the measurement of the metric gram.

granite
A pink-colored, felsic, plutonic rock that contains potassium and usually sodium feldspars, and has a quartz content of about 10%. Granite is commonly found on continents but virtually absent from the ocean basins.

granitic
Containing Granite

granular
Same as grainy.

gravel
Accumulation of small, smooth, rounded rock deposited by a stream or river.

gravity
1. The force of attraction exerted by one body in the universe on another. Gravity is directly proportional to the product of the masses of the two attracted bodies. 2. The force of attraction exerted by the Earth on bodies on or near its surface, tending to pull them toward the Earth's center.

gravity anomaly
The difference between an actual measurement of gravity at a given location and the measurement predicted by theoretical calculation.

greasy (luster)
Luster of a mineral that appears coated with grease. Some minerals are coated with chemicals to induce a greasy luster.

groin
A structure that juts out into a body of water perpendicular to the shoreline and is built to restore an eroding beach by intercepting longshore drift and trapping sand.

group
1) An aggregate of crystals. 2) Synonym of crystal group. 3) The classification order that minerals are arranged in based on their chemical structure. 4) A scientifically recognized selection of minerals similar in structure. All groups have a specific group name, and individual minerals may also be categorized. A mineral in the g...

grouping
Same as aggregate.

habit
The attributes of the appearance of a crystal or aggregate.

half-life
The time necessary for half of the atoms of a parent isotope to decay into the daughter isotope.

halides
Group of minerals containing one of the halogen elements (chlorine, fluorine, bromine, and iodine) as a building block. Most halides are soft and fragile, and some are soluble in water. Many crystallize in the isometric system.

halogen
Five chemically related elements belong in the halogen group. They are astatine, bromine, chlorine, fluorine, and iodine. Minerals that are composed of the halogen elements are known as halides.

hard water
Water rich in calcium.

hardness
The degree of resistance of a given mineral to scratching, indicating the strength of the bonds that hold the mineral's atoms together. The hardness of a mineral is measured by rubbing it with substances of known hardness.

hardness testing kit
Kit composed of minerals or rods with labeled harnesses used to scratch a mineral to test its hardness.

headland
A cliff that projects out from a coast into deep water.

heat treated
describes a mineral or gem put under intense heat to enhance color or remove flaws.

hemimorphic
describes doubly terminated crystal with two differently shaped ends.

hexagon
Polyhedron with six sides and a top and bottom base.

hexagonal bipyramid (al)
Synonym of bipyramidal hexagon

hexagonal crystal system
Any mineral that falls under the following specifications belongs to the hexagonal crystal system: Four axes, three are equal in length and lie at an angle of 120� from each other. The fourth is either longer or shorter but must be at a right angle toward the other corners.

Holocene Epoch
The second epoch of the Quaternary Period, beginning approximately 10,000 years ago and continuing to the pres-ent time. See also Pleistocene Epoch.

hook
A spit that curves sharply at its coastal end.

hopper
Crystal form exhibiting an indenting, terraced, structure penetrating towards the center.

horn
A high mountain peak that forms when the walls of three or more cirques intersect.

hornfels
A hard, dark-colored, dense metamorphic rock that forms from the intrusion of magma into shale or basalt.

horst
A block of rock that lies between two faults and has moved upward relative to the two adjacent fault blocks. See also graben.

host mineral
Mineral that is the chief constituent of a particular rock.

hot spot
An area in the upper mantle, ranging from 100 to 200 kilometers in width, from which magma rises in a plume to form volcanoes. A hot spot may endure for 10 million years or more.

hydrate
To absorb water and construct it as part of the crystal lattice.

hydration
The addition of water into a minerals' chemical structure.

hydraulic conductivity
The extent to which a given substance allows water to flow through it, determined by such factors as sorting and grain size and shape.

hydraulic gradient
The difference in potential between two points, divided by the lateral distance between the points.

hydraulic lifting
The erosion of a stream bed by water pressure.

hydrocarbon
A molecule that is entirely made up of hydrogen and carbon.

hydrochloric acid
(HCl) Corrosive acid used mainly for dissolving unwanted substances. It is a very destructive liquid and will destroy many minerals.

hydrofluoric


hydrogen bond
An intermolecular bond formed with hydrogen.

hydrologic cycle
The perpetual movement of water among the mantle, oceans, land, and atmosphere of the Earth.

hydrolysis
A form of chemical weathering in which ions from water replace equivalently charged ions from a mineral, especially a silicate.

hydrometallurgy
The separation of metals from ore or from alloys through a process in which a liquid is the primary factor, or the forming of alloys and purification of metals through a process in which a liquid is the primary factor.

hydrothermal deposit
A mineral deposit formed by the precipitation of metallic ions from water ranging in temperature from 50� to 700�C.

hydrous
Containing water, and in some cases, containing hydroxyl.

hydroxides
Compounds of metallic elements combined with water (H2O) or hydroxyl (OH). The hydroxides are a subgroup of the oxide group.

hydroxyl
Radical composed of hydrogen and oxygen, formula = (OH).

hygroscopic
Describing a mineral that intakes and retains water from the atmosphere, and forms part of its structure. Hygroscopic minerals should be kept away from humid areas and water, and should preferably be kept in rice or silica gel which absorb moisture, since water can destroy such minerals.

hypothermal vein
Vein created at extreme depths and at a very high temperature.

ice age
A period during which the Earth is substantially cooler than usual and a significant portion of its land surface is covered by glaciers. Ice ages generally last tens of millions of years.

ice cap
An alpine glacier that covers the peak of a mountain.

icosahedron
Twenty sided polyhedron; all sides are equidimensional. Minerals shaped as icosahedrons belong to the isometric system.

icosi-tetrahedron
Synonym of trisoctahedron

idiochromatic
Exhibiting only a single color. Minerals that are monochromatic occur in only one color, no matter what specimen. Same as monochromatic.

igneous
Of volcanic origin.

igneous rock
A rock made from molten (melted) or partly molten material that has cooled and solidified.

impurity
An item present in a mineral which is not part of its integral structure, and may change its optical properties, such as color.

inclusion
Materials that are locked inside a mineral as it is forming.

incrust
To form a crust over.

incrustation
1. A pseudomorph occurring when a mineral forms a coating over another mineral, and the coated mineral dissolves. This leaves a hollow cast of the mineral that coated the dissolved mineral. 2. A crusty coating.

index fossil
The fossil of an organism known to have existed for a relatively short period of time, used to date the rock in which it is found.

index of refraction
Synonym of refractive index

indiscernable
Not noticeable.

infiltration
A pseudomorph occurring when some atoms of a mineral are replaced by different atoms forming another mineral.

inorganic
Not containing any organic substances.

inorganic chemical sediment
Sedimentary rocks - such as limestone, chert, and evaporates - that forms when the dissolved products of chemical weathering precipitate from solution. The ornate columns of travertine in caves is one example of an inorganic chemical sedimentary rock.

inosilicates
Group of silicate minerals that have their tetrahedrons form single or multiple chains, with two oxygen atoms of each tetrahedron part of its neighboring tetrahedron forming long, thin, chains.

inselberg
A steep ridge or hill left when a mountain has eroded and found in an otherwise flat, typically desert plain.

insoluble
Not able to be dissolved.

intaglio
Gemstone carved into a cameo, but instead of the engraving raised above the background, as in the cameo, the engraving is etched into the background.

intermediary
Describing a mineral midway between two mineral of a series. For example, the mineral Olivine - (Mg,Fe)2SiO4 - is midway between Forsterite - Mg2SiO4 - and Fayalite - Fe2SiO4 - in the Olivine Group.

intermolecular bonding
The act or process by which two or more groups of atoms or molecules combine due to weak positive or negative charges that develop at various points within each group of atoms due to uneven distribution of their electrons. The side of the molecule where electrons are more likely to be found will have a slight negative charge, and the side where the...

internal deformation
The rearrangement of the planes within ice crystals, due to pressure from overlying ice and snow, that causes the downward or outward flow of a glacier.

intrusive rock
An igneous rock formed by the entrance of magma into preexisting rock.

ion
An atom that has lost or gained one or more electrons, thereby becoming electrically charged.

ionic bond
The combination of an atom that has a strong tendency to lose electrons with an atom that has a strong tendency to gain electrons, such that the former transfers one or more electrons to the latter and each achieves chemical stability under the octet rule. The atom that loses electrons acquires a positive electric charge and the atom that gains ele...

ionic bonding
The act or process of forming of an ionic bond.

ionic substitution
The replacement of one type of ion in a mineral by another that is similar to the first in size and charge.

iridesce
The present term describing something displaying iridescence.

iridescence
Light effect causing a mineral to display a play of colors on an apparently monocolored surface. Iridescence is many times the result of pearly luster, seen around an area where pressure occurred, displaying a similar image to that of fresh oil rising to the surface of a road at the beginning of a rain. Iridescence is also the result of mild tarnis...

irradiation
The act of being exposed to radiation. This may have an effect on several gemstones by altering their color.

irridium
A rare earth metal often alloyed with Platinum for jewelry at either 5 or 10 percent to raise the its hardness. Interestingly, Iridium is thought to be more common in extraterrestrial matter than on Earth, and is the most important piece of evidence linking the extinction of the dinosaurs with an asteroid strike becaus...

isometric crystal system
Any mineral that falls under the following specifications belongs to the isometric crystal system: Three axes, all of them are equal in length and lie at 90� from the other.

isomorphism
Having the same crystal form, meaning that the molecular arrangement is identical, except for the fact that different elements are present. If two minerals are isomorphous to each other, than they contain different elements arranged in the same arrangement and number, such as Calcite (CaCO3) and Siderite (FeCO3<...

isostasy
The equilibrium maintained between the gravity tending to depress and the buoyancy tending to raise a given segment of the lithosphere as it floats above the asthenosphere.

isotope
One of two or more forms of a single element; the atoms of each isotope have the same number of protons but different numbers of neutrons in their nuclei. Thus isotopes have the same atomic number but differ in atomic mass.

isotope dating
The process of using relative proportions of parent to daughter isotopes in radioactive decay to determine the age of a given rock or rock stratum.