Glossary of Rock and Mineral Terms - C
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- Gem or stone without facets that is highly polished and has smooth, rounded
edges. (See our How
To Cab online guide)
- Containing the compound calcium carbonate.
- Containing calcium.
- calcite (group)
- Group of minerals belonging to the carbonate group that are isomorphous with
one another and have the same properties, such as that they all:
1. Crystallize in the trigonal sect of the hexagonal system, and most commonly
form rhombohedrons and scalenohedrons.
2. Have perfect rhombohedral cleavage
3. Exhibit a very strong double refraction in transparent rhombohedrons
- A vast depression at the top of a volcanic cone, formed when an
eruption substantially empties the reservoir of magma beneath the
cone's summit. Eventually the summit collapses inward, creating a caldera. A
caldera may be more than 15 kilometers in diameter and more than 1000 meters
- A white soil horizon consisting of calcium carbonate, typical of arid and
semi-arid areas. Brief heavy rains dissolve calcium carbonate in the upper
layers of soil and transport it downward; the rainwater then evaporates
rapidly, leaving the calcium carbonate to form a new, solid layer of soil.
- Gem with a design or figure carved out of the stone, and raised above the
- The ability of a given stream to carry sediment, measured as
the maximum quantity it can transport past a given point on the channel bank
in a given amount of time. See also competence.
- Aggregate composed of tiny, thin, straight, long crystal strands; hair like.
- capillary fringe
- The lowest part of the zone of aeration, marked by the rising of
water from the water table due to the attraction of the water molecules to
mineral surfaces and other molecules, and to pressure from the zone of
- carbon-14 dating
- A form of isotope dating that relies on the 5730-year half-life of
radioactive carbon-14, which decays into nitrogen-14, to determine the age of
rocks in which carbon-14 is present. Carbon-14 dating is used for rocks from
100 to 100,000 years old.
- One of several minerals containing one central carbon atom with strong covalent
bonds to three oxygen atoms and typically having ionic bonds to one
or more positive ions.
- 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.
- carbonates (group)
- 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 into Calcite Group and
Aragonite Group. The Nitrates and Borates are sometimes considered a category
of the carbonates.
- carlsbad twin
- Form of penetration twinning where two Orthoclase crystals form
interpenetrating twins as depicted in the figure below.
- Ornamental figure, such as a stone lion, carved out of a rock or mineral. A
piece of stone formed this way is described as carved.
- cassiterite twin
- Two crystals that twin in a repeated pattern ("repeated twinning")
as depicted in the figure below. Named after the mineral Cassiterite, which
most frequently exhibits this form of twinning.
- The hypothesis that a series of immense, brief, worldwide upheavals changed
the Earth's crust greatly and can account for the development of mountains,
valleys, and other features of the Earth. See also uniformitarianism.
- Neutral atom that loses an electron and becomes positively charged.
- cats eye
- 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".
- cave (cavern)
- A naturally formed opening beneath the surface of the Earth, generally
formed by dissolution of carbonate bedrock. Caves may also form by
erosion of coastal bedrock, partial melting of glaciers, or solidification of
lava into hollow tubes.
- Hollow area in rock that develops because of some form of stress. Many
cavities are lined with crystals. See also vug.
- The diagenetic process by which sediment grains are bound together by
precipitated minerals originally dissolved during the chemical
weathering of preexisting rocks.
- cementation zone
- Underground area where certain elements are concentrated and can combine to
form new, or primary, minerals.
- Cenozoic Era
- The latest era of the Phanerozoic Eon, following the Mesozoic Era and
continuing to the present time, and marked by the presence of a wide variety
of mammals, including the first hominids.
- chemical sediment
- Sediment that is composed of previously dissolved minerals that have
either precipitated from evaporated water or been extracted from water by
living organisms and deposited when the organisms died or discarded their
- chemical weathering
- The process by which chemical reactions alter the chemical composition of
rocks and minerals that are unstable at the Earth's surface and convert them
into more stable substances; weathering that changes the chemical
makeup of a rock or mineral. See also mechanical weathering.
- center of symmetry
- 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. Chatoyant is the
ability to exhibit chatoyancy.
- A substance with a distinct molecular formation, produced by a chemical
- chemical bond
- A force by which atoms are bound in a molecule or crystal.
- chemical formula
- The scientific method of describing what elements a material is composed of.
- chemical structure
- The atomic arrangement of a substance.
- The study and science of the composition and structure of all substances.
- A member of a group of sedimentary rocks that consist primarily of
microscopic silica crystals. Chert may be either organic or inorganic, but the
most common forms are inorganic.
- Small nuggets of rocky material that exist in certain meteorites. These
droplets of matter are believed to have condensed from our solar system's
original nebula about five billion years ago. Their primary element is iron.
- chromate (group)
- 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.
- chrysoberyl twin
- Form of contact twinning, in which six Chrysoberyl crystals join at the
base, forming a six-pointed formation, as depicted in the figure below.
- cinder cone
- A pyroclastic cone composed primarily of cinders.
- A deep, semi-circular basin eroded out of a mountain by an alpine glacier.
- cirque glacier
- A small alpine glacier that forms inside a cirque, typ-ically
near the head of a valley.
- Fragment of rock or mineral broken off from a large piece.
- Being or pertaining to a sedimentary rock composed primarily from
fragments of preexisting rocks or fossils.
- 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 tendency of certain minerals to break along distinct planes in their crystal
structures where the bonds are weakest. Cleavage is tested by striking or
hammering a mineral, and is classified by the number of surfaces it produces
and the angles between adjacent surfaces.
- cleavage angle
- The angle, or side, that exhibits or has exhibited cleavage.
- cleavage fragment
- Crystallized fragment that broke off of a mineral that exhibits cleavage.
- cleaved surface
- Broken surface of a mineral that has a flat surface where the mineral broke,
proving that the mineral exhibits cleavage.
- Describing an elongated crystal with a steep, slanted angle towards its top
at the base. Minerals shaped this way are clinopinicoidal.
- Dense agglomeration of crystals.
- A member of a group of easily combustible, organic sedimentary rocks
composed mostly of plant remains and containing a high proportion of carbon.
- The area of dry land that borders on a body of water.
- A thin layer of one mineral on the surface of another.
- A high mountain pass that forms when part of an arête erodes.
- The characteristic color or colors of a mineral.
- Aggregate defining a mineral which has parallel, slender, compact, adjoining
- The diagenetic process by which the volume or thickness of sediment
is reduced due to pressure from overlying layers of sediment.
- The ability of a given stream to carry sediment, measured as
the diameter of the largest particle that the stream can transport. See also capacity.
- composite cone
- See stratovolcano.
- The elements and the quantity of the elements a substance contains.
- An electrically neutral substance that consists of two or more elements
combined in specific, constant proportions. A compound typically has physical
characteristics different from those of its constituent elements.
- Stress that reduces the volume or length of a rock, as that produced
by the convergence of plate margins.
- 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.
- conchoidal fracture
- Mineral fracture in which the indentation resembles a shell.
- Aggregate composed of a mass of small crystals that become cemented
together, resulting in a rounded, odd form.
- 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.
- cone of depression
- An area in a water table along which water has descended into a well
to replace water drawn out, leaving a gap shaped like an inverted cone.
- A clastic rock composed of particles more than 2 millimeters in
diameter and marked by the roundness of its component grains and rock
- contact metamorphism
- Metamorphism which is caused from magma intrusion near the contact
with the magma.
- contact twinning
- Form of twinning where two crystals join together at a base. Examples:
japanese twin, spinel twin, and chrysoberyl twin.
- continental collision
- The convergence of two continental plates, resulting in the formation
of mountain ranges.
- continental drift
- The hypothesis, proposed by Alfred Wegener, that today's continents broke
off from a single supercontinent and then plowed through the ocean floors into
their present positions. This explanation of the shapes and locations of
Earth's current continents evolved into the theory of plate tectonics.
- continental ice sheet
- An unconfined glacier that covers much or all of a continent.
- continental platform
- Continental platforms are the regions adjacent to and surrounding the
continental shields. They are typically a relatively thin veneer of
sedimentary rock that buries the edges of the shields.
- continental shield
- Broad areas of exposed ancient crystalline rocks in the cores of the Earth's
continents. These rocks are typically the oldest on the continentes, many more
than 2.5 billion years old.
- convection cell
- The cycle of movement in the asthenosphere that causes the plates of
the lithosphere to move. Heated material in the asthenosphere becomes
less dense and rises toward the solid lithosphere, through which it cannot
rise further. It therefore begins to move horizontally, dragging the
lithosphere along with it and pushing forward the cooler, denser material in
its path. The cooler material eventually sinks down lower into the mantle,
becoming heated there and rising up again, continuing the cycle. See also plate
- The coming together of two lithospheric plates. Convergence causes subduction
when one or both plates is oceanic, and mountain formation when both plates
are continental. See also divergence.
- 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, consisting primarily of pure metals such
as iron and nickel. The core is the densest layer of the Earth, and is divided
into the outer core, which is believed to be liquid, and the inner core, which
is believed to be solid. See also crust and mantle.
- The process of determining that two or more geographically distant rocks or
rock strata originated in the same time period.
- covalent bond
- The combination of two or more atoms by sharing electrons so as to achieve
chemical stability under the octet rule. Atoms that form covalent bonds
generally have outer energy levels containing three, four, or five electrons.
Covalent bonds are generally stronger than other bonds.
- Aggregate composed of flaky or tabular crystals that seem adjoined from a
base; with grooves between long, slender, arc-like crystals.
- A hole that was created in the earth or celestial body from the impact of a
- The segment of the Earth's continents that have remained tectonically stable
and relatively earthquake-free for a vast period of time. The craton is
composed of the continental shield and the surrounding continental platform.
- Condition in opal that causes it to form small, internal cracks, and in some
severe cases will eventually disintegrate the opal.
- The slowest form of mass movement, measured in millimeters or centimeters
per year and occurring on virtually all slopes. cross bed A bed made up of
particles dropped from a moving current, as of wind or water, and marked by a
downward slope that indicates the direction of the current that deposited
- 1. The outermost layer of the Earth, consisting of relatively low-density
rocks. See also core and mantle.
2. A disorganized, crusty, mineral coating that can be thin or thick.
3. Type of aggregate.
- Aggregate of a crust coating on a rock or mineral.
- Composed of tiny, microscopic crystals.
- A mineral in which the systematic internal arrangement of atoms is outwardly
reflected as a latticework of repeated three-dimensional units that form a
geometric solid with a surface consisting of symmetrical planes.
- crystal angle
- The sum of the angles on a crystal edge that are characteristic to a crystal
- crystal class
- 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
- crystal face
- The side of a crystal. The number of faces varies with the crystal's
- crystal form
- The shape and habit of a particular crystal.
- crystal habit
- The habitual form that a mineral forms it crystallizes.
- crystal lattice
- The arrangement of atoms in a crystal, giving each crystal its distinct
shape. See also crystal structure.
- crystal structure
- 1. The geometric pattern created by the systematic internal arrangement of
atoms in a mineral.
2. The systematic internal arrangement of atoms in a
- crystal system
- 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.
- 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.
- Containing a crystal form. May also be referred to molten rock that
solidifies and forms a crystal shape.
- The science and study of crystal structure. Person who studies
crystallography is a crystallographer.
- Abbreviation for carat
- Six sided polyhedron; all sides are equi-dimensional and bisect at 90º.
Minerals shaped as cubes belong to the isometric system.
- cubic crystal system
- Synonym of isometric system.
- cubic cleavage
- 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.
- 1. n A description of the type of facet.
2. v Meaning faceted.
- cyclosilicates group
- 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.
- cymophone effect
- Phenomenon seen on a few polished gems that cause it to exhibit a floating
light reflection that moves as the gem is rotated.