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    -   by George Campbell    (


Accessory - A mineral occurring in small amounts, in addition to the primary mineral on a specimen.
Acicular - Needle-shaped. Generally very slender crystals, often in clusters.
Adamantine - Having a diamond-like luster. The brightest luster in minerals.
Aesthetic Specimen - A mineral specimen displaying an exceptionally attractive form.
Aggregate - A group of crystals of one or more minerals.
Alteration - A change in a mineral caused by some influence, often creating a new species. As in Laumontite altering to become Leonhardite by dehydration.
Amorphous - Lacking crystalline structure, as in Amber.
Amygdule - A small cavity in a rock, often lined or filled with crystals.
Anhedral - Showing no typical crystal form or crystal faces.
Arborescent - Having a branching, tree-like habit or form.
Arsenates - Minerals containing the arsenate (AsO4) radical as a major component. (Adamite)
Axis - An imaginary line passing through a crystal symmetrically

Basal - Parallel to the top or bottom of a crystal.
Basal Pinacoid - A flat face at the top or bottom of a crystal in some systems.
Birefringence - The degree of double refraction in a crystal. (Calcite)
Blady - A flattened habit resembling a knife blade. (Barite)
Borates - Minerals containing the borate (BO3) radical as a major component. (Colemanite)
Botryoidal - Having a medium-sized rounded form, as in a cluster of grapes.
Brittle - Easily broken or fractured.

Cabinet Specimen - A specimen over 8 cm in size, suitable for display in a cabinet.
Capillary - Hair-like habit. (Cuprite var. Chalcotrichite)
Carbonates - Minerals containing the carbonate (CO3) radical as a major component. (Calcite)
Cleavage - Planes in a crystal which are easily split.
Cleavage Face - A face on a specimen caused by cleavage, rather than natural growth.
Columnar - Like a column. Usually referred to in groups of parallel, rod-shaped crystals.
Conchoidal Fracture - Shell-shaped breakage pattern, as in glass or quartz.
Crested - Tabular crystals in groups, which form ridges.
Cruciform - Having the shape of a cross (Staurolite)
Crystal - A solid mineral, having a definite form bound by flat faces.
Cryptocrystalline - Having crystals too small to be seen without a microscope. (Chalcedony)
Cyclical Twin - A twinned crystal made up of multiple individual crystals, often forming a pseudosymetrical form such as a hexagon. (Aragonite, Chrysoberyl)

Dana - A reference to some edition of Dana's System of Mineralogy, now in 8th Edition.
Dana Locality-- A locality specifically mentioned in Dana's System, any edition, for a mineral.
Dehydration - A tendency for a mineral to lose it's water content, often altering to a different species.
Dendritic - Made up of dendrites, or fern-like branching structures.
Diaphaneity - Synonym for transparency
Discoidal - A round, disk-shaped habit, thicker in the middle than at the edges.
Dodecahedron - A twelve-sided crystal in the Isometric system.
Dome - A crystal form parallel to one of the lateral axes and intersecting the other two.
Double Refraction - An optical phenomenon of some minerals which splits rays of light into two rays.
Double-Terminated - A crystal displaying termination faces on both ends.
Druse, Drusy - A covering of tiny crystals of a mineral, generally with only termination faces visible.
Ductile - Capable of being drawn into a thin wire.

Earthy - Fine grained and powdery, with a dull luster.
Efflorescence - A powdery crust, created by evaporation
Elastic - Capable of being bent, then returning to original shape.
En Echelon -- Pattern of growth of a group of parallel crystals showing a set of faces arranged in a row.
Epitaxy - Crystals growing on another crystals, in alignment with the crystal structure of the host crystal.
Equant - A crystal having all sides approximately of equal size
Euhedral - A crystal showing well-formed faces, generally complete.

Felted - Having a fibrous, matted habit, like felt. (Palygorskite)
Fibrous - Thread-like habit, usually matted. (Actinolite, Asbestos)
Filiform - Thin wire or hair-like habit. (Millerite)
Flexible - Can be bent, but does not return to original shape.
Fluorescent - Emits colored light when stimulated by ultraviolet or other energy source.
Foliated - Leaf like structure, which can be easily separated into leaves. (Micas)
Fracture - Uneven breakage of a mineral, leaving a rough surface rather than a cleavage plane.
Friable - Crumbly

Geniculated - Showing a knee-like bend or bends. (Rutile)
Geode - A rounded rock with a cavity filled or lined with another mineral.
Glassy - A luster, slightly less bright than Adamantine. (Quartz)
Globular - Rounded habit, usually somewhat irregular.
Granular - Having a structure made up of small grains.

Habit - The shape and stucture of a mineral's crystal or cluster of crystals.
Hackly Fracture - A jagged fracture, with an irregular surface. (Copper)
Halides - Minerals containing the halogen elements, Chlorine, Bromine, Fluorine, and Iodine, as primary elements. (Halite, Fluorite)
Hardness - The relative resistance of a mineral to being scratched. Measured in Moh's units, with Talc having a hardness of 1 and Diamond having a hardness of 10. A logarithmic scale.
Hemimorphic - A crystal having different forms at each end. (Tourmaline, Hemimorphite)
Hexagonal System - A crystallization system having three equal horizontal axes intersecting at 120 degrees, plus a vertical axis of a different length. (Calcite, Beryl, Quartz, etc.)
Hydrothermal - Deposited from a hot solution, generally heated by magmatic heat.
Hygroscopic - Tending to absorb water, thus altering a specimen. (Hanksite)

Inclusion - A foreign substance contained in a mineral. Can be another mineral, liquid, or air.
(Rutilated Quartz)
Iridescence - Play of prismatic colors on the surface of a mineral. (Goethite, Lepidochrosite)
Isometric System - A crystallization system having three equal-length axes at 90 degrees to each other.
(Pyrite, Garnet, Fluorite, etc.)

Japan Law Twin -- A particular twinned form in quartz, with two crystals joining each other at an angle of about 84 degrees. The individual crystals are often flattened prisms.

Keystone - A wholesaler's term, usually meaning half the marked price for a quantity purchase.

Label - An essential component of any specimen. Old labels are desirable.
Lamellar Structure - Made up of thin plates (lamella) or scales.
Large Cabinet Specimen - Generally a specimen over 10 cm in size.
Lenticular - A round habit, having the form of a convex lens.
Locality - The specific place a specimen was found. The more detailed, the better.
Luster - The relative surface reflectivity of a specimen. Adamantine is the highest, ranging to dull.
LWUV - Long Wave Ultra Violet light. One form of Ultraviolet light used to display fluorescence.

Malleable - Capable of being hammered into thin sheets. (Gold, Silver)
Mammillary - A habit made up of large, curved surfaces. (Hematite)
Massive - Having no discernable regular crystal form.
Massively Crystalline - Irregular form, showing crystal or cleavage faces, but with no euhedral crystals.
Matrix - The rock or mineral surrounding a particular crystal or group of crystals.
Metallic - Having a luster resembling polished metal (Specular Hematite, Galena)
Metamict - Having lost crystal structure due to the influence of radioactivity, while retaining the outward form of the crystal.
Micaceous - A habit of easily separated lamellae. Mica-like.
Microcrystalline - Having crystal grains only visible under a microscope.
Micromount - A small specimen, generally under 1cm in size, for microscopic examination.
Miniature - A specimen ranging in size from 4-8 cm.
Modified Face - A crystal face truncated by another face, as in an octahedron modified by a cube.
Molybdates - Minerals containing the molybdate (MoO4) radical as a major component. (Wulfenite)
Monoclinic System - A crystallization system having three unequal axes, two at an oblique angle and
a third at right angles to those two. (Gypsum, Orthoclase, etc.)
Museum Specimen - Usually a very large specimen, often showing spectacular crystals or form.

Native Element - A mineral made up of just one element. (Gold, Sulfur)
Nitrates - Minerals containing the Nitrate (NO3) radical as a major component.
Nodular - A habit displaying small, irregular lumps.
Nonmetallic - Having a luster not like metal.
Nugget - A rounded or irregular lump of a mineral, usually a native metal. (Gold, Platinum)

Ocherous - Powdery, earthy habit.
Octahedron - An eight-sided crystal of the Isometric System (Diamond, Pyrite)
Oolitic - Habit made up of small rounded grains (oolites)
Opalescence, Opalescent - Showing an internal play of colors or iridescence. (Opal)
Opaque - Not allowing the transmission of any light through a mineral.
Oxides - Minerals containing a metal and oxygen as the main components. (Cuprite, Corundum)

Paragenesis - The association and order of formation of minerals in a specimen or deposit.
Paramorph - A mineral which derives from another mineral, but having the same chemical composition.
Parting - The ability of a mineral to separate along definite directions, along twinning or gliding planes.
Pearly - A luster description showing a glimmering sheen as in the surface of a pearl.
Pegmatite - A coarsely crystalline area in an igneous formation. Many gem minerals form in pegmatites.
Penetration Twin - A twinned crystal where one crystal has intergrown with another. (Fluorite, Pyrite)
Perky Box -- A cubic-shaped plastic box with a black base, used for mounting thumbnail specimens.
Phantom - A crystal which shows an internal image of a crystal, caused by color zoning or inclusions
Phosphates - Minerals containing the phosphate (PO4) radical as a major component. (Apatite)
Phosphorescence - A lingering emission of light following exposure to Ultraviolet light or other energy.
Pinacoid - A crystal face parallel to two crystal axes (three in the hexagonal system).
Pisolitic Habit - Like a cluster of rounded grains, about the size of a pea.
Placer Mineral - A mineral found in stream beds, among the gravel and sand. (gold, platinum, corundum)
Pleochroic - Showing different colors when a crystal is viewed from different directions.
Plumose Habit -- A feather-like habit.
Prism - A crystal face intersecting lateral axes, and parallel to the vertical axis.
Prismatic - An elongated crystal form in which the prism faces are prominent, as in the typical quartz crystal.
Pseudomorph - A mineral which has replaced another mineral, assuming the form of the replaced mineral.
Pyramid - A crystal face intersecting three crystal axes.
Pyramidal - A crystal primarily showing the pointed ends, but little or no prism faces.

Quarry - An open or surface mine, generally used to extract rock for building stone or gravel.

Radial Habit - A habit with slender crystals radiating out from a central point.
Reference Specimen - A specimen which lacks aesthetic qualities, suitable for study, but not display.
Reniform Habit -- A habit showing large rounded shapes, between botryoidal and mammillary in size.
Resinous Luster - A luster similar to the resin exuded from plants. (Sphalerite)
Reticulated - A habit made up of slender crystals crossing each other in a network pattern. (Cerussite)
Rhombohedron - A crystal having six sides, each of which forms a parallelogram. (Hexagonal system)

Scalenohedron - A crystal in the hexagonal system displaying irregular triangular faces. (Calcite)
Scepter Crystal - A compound crystal where a larger crystal has grown atop a smaller prismatic crystal.
Schiller - An irridescent luster, as in some feldspars (Labradorite)
Schistose - Thinly layered, as in schist rocks.
Sectile - Capable of being cut with a knife (Acanthite)
Silky - A fibrous sort of luster, often display chatoyancy (Gypsum)
Silicates - Mineral containing silicon and oxygen, along with other elements.
Skarn - A contact metamorphic rock, often containing well-formed crystals of silicate and other minerals.
Skeletal - Crystal habit showing hollowed out faces caused by uneven growth. (Halite)
Space Lattice - The three-dimensional lattice of atoms making up the structure of a crystal.
Specular - Brilliantly reflective, mirror-like (Hematite)
Splendent - Brightly shining
Stellate - Having a star-shaped habit
Streak - The color a mineral displays when finely powdered, or rubbed on a porcelain plate.
Striated - Having parallel lines on the surface (Quartz, Pyrite)
Sulfates - Minerals containing the sulfate (S04) radical as a major component. (Gypsum, Barite)
Sulfides - Minerals which are compounds of a metallic element with sulfur.
Sulfosalts - Minerals which are a combination of a semi-metal, such as arsenic, and sulfur, along with a metallic element. (Enargite, Pyrargyrite)
SWUV - Short Wave of the frequencies of ultraviolet light causing fluorescence in minerals.

Tabular - A habit displaying a flattened form. (Wulfenite)
Tenacity - The resistance of a mineral to breakage.
Termination - Crystal faces at the end of a crystal axis.
Tetragonal System - Crystallization system having two equal horizontal axes at right angles to each other, and a vertical axis of a different length at right angles to the other two. (Zircon, Cassiterite)
Thumbnail - A specimen ranging in size between 1 and 3 cm. Generally mounted in a cubic plastic box.
Tough - Difficult to break or fracture
Translucent - Capable of transmitting some light, but cannot be seen through.
Transparent - Capable of being seen through.
Triclinic System - Crystallization system having three unequal axes at oblique angles to each other. (Microcline, Rhodonite)
Trilling - A cyclical twin made up of three crystals, generally forming a hexagonal outline. (Crysoberyl)
Tungstates - Minerals containing the tungstate (WO4) radical as a major component. (Scheelite)
Twinned Crystal - A compound crystal made up of two or more individual crystals integrown according to one of the twin laws along a common plane.
Type Locality - The locality where the first described specimen of a mineral was found.

Unit Cell -- The smallest part of a crystal lattice structure which has all the elements of the structure of that lattice.

Vanadates - Minerals containing the vanadate (VO4) radical as a major components.
Variegated - Displaying a range of different colors (Agate)
Vitreous - Having a luster resembling glass.
Vug - An open cavity in matrix, lined with crystals.

Waxy - Having a luster resembling wax (Smithsonite)

X-Ray Diffraction (XRD) - A method of analyzing the structure of a mineral by examining the pattern created when x-rays are passed through a crystal of the mineral.


Zeolites - Aluminosilicate minerals which can lose or regain water without losing without changing their crystal structure.
Zonal Structure - A structure showing bands or concentric layers.