Iron smelted entirely from raw ore. Standard, 2
A collective term introduced by Folk (1959) for one of several varieties
of discrete and organized carbonate aggregates that serve as the coarser
framework grains in most mechanically deposited limestones, as
distinguished from sparry calcite (usually cement) and carbonate-mud
matrix (micrite). Important allochems include silt-, sand-, and
gravel-size fragments torn up and reworked from the deposit; ooliths;
pellets; lumps; and fossils or fossil fragments (carbonate skeletons,
shells, etc.). Syn:allochemical
See:allochem
a. A calcium-chromium garnet. Fay
b. A reddish brown variety of andradite garnet.
a. Descriptive of crystals that exhibit electrical conductivity under the
influence of light. Hess
b. A gem stone with a coloring agent extraneous to its chemical
composition. Opposite of idiochromatic. Hess
c. Color produced by a chromophore that is not essential to mineral
composition.
Mineral that would be colorless if chemically pure, but which commonly
exhibits a range of colors due to the presence of small quantities of one
or more coloring elements. Chief among these elements are those having
atomic numbers 22 to 29; namely, titanium, vanadium, chromium, manganese,
iron, cobalt, nickel, and copper. Corundum, beryl, spinel, and quartz are
examples of allochromatic gemstones. See also:idiochromatic mineral
Anderson
a. A mass of rock that has been moved from its place of origin by tectonic
processes, as in a thrust sheet or nappe. Many allochthonous rocks have
been moved so far from their original sites that they differ greatly in
facies and structure from those on which they now lie. Ant. autochthon.
Syn:allochthonous
b. A mass of redeposited sedimentary materials originating from distant
sources. AGI
a. Originated by Gumbel and applied to rocks, the dominant constituents of
which have not been formed in place. CF:autochthonous
Holmes, 1
b. Coal formation according to the drift theory. Nelson
c. Formed or produced elsewhere than in its present place; of foreign
origin, or introduced. The term is widely applied; e.g., to coal or peat
that originated from plant material transported from its place of growth,
or to an allochthon on a low-angle thrust fault. The term is similar in
meaning to allogenic, which refers to constituents rather than whole
formations. Ant. autochthonous. See also:allochthon
Coal originating from accumulations of plant debris that have been
transported from their place of growth and deposited elsewhere. The debris
can be differentiated as coming from near or from far, and likewise
whether it represents recent (dead or still living) or already fossilized
material. Syn:drift coal
AGI; Tomkeieff
Drift peat of lacustrine character. It is subdivided into Gyttja type and
Dry type. Tomkeieff
A monoclinic mineral (Co,Fe)AsS ; steel gray; dimorphous with glaucodot.
Formerly called alloclase.
See:volcanic breccia
Generated elsewhere; applied to those constituents that came into
existence outside of, and previously to, the rock of which they now
constitute a part; e.g., the pebbles of a conglomerate. CF:authigenic
Holmes, 2
See:herderite
Of the same crystalline form but of different chemical composition.
Syn:isomorphous
a. Syn:paramorph (obsolete); pseudomorph. AGI
b. A polymorph or dimorph. Adj. allomorphous.
Changes produced in minerals without gain or loss of components; e.g., the
change from kyanite to sillimanite. See also:paramorphism
Obsolete term for barite, esp., pseudomorphous after anhydrite.
Of the same chemical composition but of different crystalline form.
CF:allomeric
a. A nearly silver-white palladium, found in hexagonal plates in the Harz
Mountains, Germany. Fay
b. Former name for stibiopalladinite.
c. Palladium crystallizing in the hexagonal system (as opposed to
isometric palladium).
a. Al2 O3 .SiO2 .nH2 O . A clay mineral
composed of hydrated aluminosilicate gel of variable composition; P (sub
2) O5 may be present in appreciable quantity. Syn:riemannite
McGraw-Hill, 1
b. A mineral gel, amorphous hydrous aluminum silicate; soft; has pale
tints; in soils developed from volcanic glass and ash. It changes from
glassy to earthy upon dehydration.