Refers to vegetable accumulations laid down on a wet substratum in
contrast to those deposited under water. CF:phenhydrous
Said of a rock of compact texture, composed of extremely small, fragmental
particles that are barely visible under a microscope.
a. Said of the texture of a rock consisting of crystals that are too small
to be recognized and separately distinguished even under the ordinary
microscope (although crystallinity may be shown by use of the electron
microscope); indistinctly crystalline, as evidenced by a confused
aggregate effect under polarized light. Also, said of a rock with such a
texture. Syn:microaphanitic; microcryptocrystalline; microcrystalline;
microfelsitic. CF:dubiocrystalline
b. Said of a rock or rock texture of a crystalline rock in which the
crystals are too small to be recognized megascopically. This usage is not
recommended until crystallinity can be established by polarized-light
microscopy or X-ray diffraction. Syn:aphanitic
c. Descriptive of a crystalline texture of a carbonate sedimentary rock
having discrete crystals with maximum diameters variously set at 1 mu m, 4
mu m, and 10 mu m.
A nongenetic, descriptive term for a roughly circular structure formed by
the sudden, explosive release of energy and exhibiting intense, often
localized rock deformation with no obvious relation to volcanic or
tectonic activity. Many cryptoexplosion structures are believed to be the
result of impact of meteorites of asteroidal dimensions; others may have
been produced by volcanic activity. The term largely replaces the earlier
term cryptovolcanic structure. AGI
a. Denoting a texture of rocks so fine that the individual constituents
cannot be distinguished under a microscope. Usually the result of a
cryptocrystalline intergrowth of quartz and feldspar.
See also:cryptocrystalline
b. Having a graphic texture of intergrowths too small to be resolved with
a light microscope.
An isometric mineral, (NH4 )2 SiF6 ; dimorphous with
bararite.
The conditions under which coal was formed. Decay under water in swamps.
Tomkeieff
Said of a hydrothermal mineral deposit without demonstrable relationship
to igneous processes. The term is little used. CF:apomagmatic;
telemagmatic. AGI
a. A monoclinic mineral, K(Mn4+ , Mn2+ )8 O (sub
16) ; pseudotetragonal. CF:psilomelane
b. The mineral group coronadite, cryptomelane, hollandite, manjiroite, and
priderite.
See:aphanite
a. A very fine crystalline texture. Stokes
b. Of or pertaining to cryptomere. Johannsen
Extremely fine-grained perthite with submicroscopic lamellae (1 to 5 mu m)
detectable only by X-ray diffraction or electron microscopy. The K-rich
host may be sanidine, orthoclase, or microcline; the Na-rich phase may be
albite or analbite. CF:perthite; microperthite.
A circular structure lacking evidence of shock metamorphism or of
meteorite impact and therefore presumed to be of igneous origin, but
lacking exposed igneous rocks or obvious volcanic features; a rock
structure produced by concealed volcanic activity. Preferred term:
cryptoexplosion structure. AGI
a. Eon of hidden life. Syn. of Precambrian. AGI
b. That part of geologic time represented by rocks in which evidence of
life is only slight and of primitive forms. CF:Phanerozoic
a. A regular polyhedral form, bounded by planes, which is assumed by a
chemical element or compound, under the action of its intermolecular
forces, which passing, under suitable conditions, from the state of a
liquid or gas to that of a solid. A crystal is characterized first by its
definite internal molecular structure and second, by its external form.
Fay
b. The regular polyhedral form, bounded by plane surfaces, which is the
outward expression of a periodic or regularly repeating internal
arrangement of atoms. See also:crystal face
c. A body formed by the solidification under favorable conditions of a
chemical element, a compound, or an isomorphous mixture and having a
regularly repeating internal arrangement of its atoms; esp. such a body
that has natural external plane faces as a result of the internal
structure. Webster 3rd
d. Quartz that is transparent or nearly so and that is either colorless or only slightly tinged. Also a piece of this material. Also called rock
crystal. Webster 3rd
e. A colorless transparent diamond. Webster 3rd
f. As an adj., consisting of or resembling crystal. Syn. for crystalline;
clear; transparent. Relating to or using a crystal. Webster 3rd
g. A regular polyhedron exhibited by a chemical element or compound where
its atomic particles assume a periodic array under suitable physical and
chemical conditions. The external form is a low-energy response to the
symmetry of the internal forces with each face parallel to a high-density
plane of atomic particles.
h. Any solid material with a periodic internal structure.
Syn:crystalline
i. Glass of superior quality and high density and luster (resulting from
inclusion of lead salts in old objects), commonly with ornamental cutting,
e.g., flint glass.
j. An adj. referring to material properties, e.g., crystal structure (for
internal periodicity), crystal solution (as between end members of a
mineral series).
A number of crystals grown together so that each crystal in the group is
large enough to be seen by the unaided eye and each crystal is more or
less perfect. In gemmology, it differs from a crystalline aggregate, as a
homogenous gem stone can be cut only from an individual crystal of a
crystal aggregate. Syn:crystal group
Imaginary lines passing through a crystal in important symmetry
directions, intersecting in the origin at the center of the crystal. The
axes are usually three in number, and they are chosen to act as a frame of
reference by means of which the relative positions of the crystal faces
can be described. Anderson
a. A reference axis used for the description of the vectorial properties
of a crystal. There are generally three noncoplanar axes, chosen parallel
to the edges of the unit cell of the crystal structure so as to be
parallel to symmetry directions if possible. AGI
b. One of three minimal noncoplanar reference lines used to describe the
vectorial properties of crystalline materials.
Syn:crystallographic axis
c. A line parallel to the intersections of crystal faces.
Syn:zone axis
d. A line about which crystal symmetry appears distributed.
Syn:symmetry axis
e. A line about which a part of a crystal appears to have rotated in a
fashion not permitted by the symmetry group of the crystal.
Syn:twin axis
Hafnium and zirconium produced by the van Arkel and de Boer process.
Thomas
Fillings of a cavity left by solution or sublimation of a crystal embedded
in a fine-grained sediment. Pettijohn, 1
The study of the relations among chemical composition, internal structure,
and the physical properties of crystalline matter. AGI