Descriptive of minerals with hexagonal habit without hexagonal symmetry;
e.g., hexagonal plates of monoclinic mica.
A name that may be applied to any mineral resembling jade in appearance;
e.g., bowenite, massive serpentine. English
Large isometric crystals consisting of mixtures of nepheline and
orthoclase, or of analcime formed as breakdown products of leucite; occurs
in syenites from Arkansas, Montana, and Brazil. CF:leucite;
metaleucite.
A monoclinic mineral, Cu5 (PO4 )2 (OH)4 ;
trimorphous with ludjibaite and reichenbachite; dark green.
Syn:dihydrite; phosphochalcite; phosphorochalcite; tagilite.
A mineral sample with the external crystal form of one mineral and the
internal chemistry of another; e.g., cubes of geothite after pyrite
resulting from oxidation of the ferrous sulfide to ferric oxyhydroxide.
CF:paramorph
Quartz displaying the form and habit of any of several mineral species,
which it has assumed through replacement. The most common quartz
pseudomorphs are those of calcite, barite, fluorite, and siderite.
Silicified wood is quartz pseudomorphous after wood.
A type of tonstein characterized by numerous pseudomorphs of
kaolinite-feldspar or kaolinite-mica within a kaolinite groundmass.
IHCP
See:porphyroblast
A compact massive mixture of chlorite minerals resembling serpentine.
a. Said of the texture of an igneous rock in which larger crystals have
developed in a macrocrystalline groundmass, but were formed, at least in
part, after the rock solidified (e.g., large potassium-feldspar crystals
in a granite). AGI
b. See:porphyroblastic
A fluid inclusion formed by healing of a fracture occurring during growth
of the host crystal. AGI
Variety of amber differing from Baltic amber in its reaction to solvents.
Tomkeieff
Said of crystal structures in which the atoms are only slightly displaced
from positions that would be in accord with a higher symmetry. Thus, a
monoclinic, pseudotetragonal mineral contains atoms only slightly
displaced from positions of tetragonal symmetry. Hess
a. Close angular approximation of a mineral with lower symmetry to one of
higher symmetry; e.g., pseudohexagonal micas with monoclinic symmetry.
b. Compound twins simulating an external symmetry not found in their
atomic structure; e.g., orthorhombic aragonite in pseudohexagonal prisms.
Syn:mimetic
c. Abnormal crystal growth along one direction; e.g., elongate native gold
cubes with apparent tetragonal symmetry.
a. A dense rock produced in the compression and shear associated with
intense fault movements, involving extreme mylonitization and/or partial
melting. Similar rocks, such as some of the Sudbury breccias, contain
shock-metamorphic effects and may be injection breccias emplaced in
fractures formed during meteoric impact. CF:ultramylonite
b. A dark gray or black rock that externally resembles tachylyte and that
typically occurs in irregularly branching veins. The material carries
fragmental clasts of adjacent rock units, and shows evidence of having
been at high temperature. Miarolitic and spherulitic crystallization has
sometimes taken place in the extremely dense devitrified base. Some
pseudotachylyte has behaved like an intrusive and has no structures
obviously related to local crushing. AGI
Quartz simulating topaz. From Striegau, Silesia, Poland. English
Viscous resistance offered by a slurry, sludge, mud, or suspension of
minerals in water as a pulp, due to the specific surface involved, with
possibly an element of thixotropy under stated conditions of pH value,
agitation, flow, temperature, and solid-to-liquid ratio. The pseudoviscous
effect is distinct from viscosity due to molecular shear. Pryor, 3
A large crater or circular hollow believed not to be associated with
volcanic activity; e.g., a crater that is possibly meteoritic in origin
but may be the result of phreatic explosion or cauldron subsidence. Adj:
pseudovolcanic. AGI
Synthetic triclinic CaSiO3 polymorphous with wollastonite-1T,
wollastonite-2M, and wollastonite-7T.
a. A general term for massive oxides of manganese not otherwise
identified; commonly botryoidal or colloform; a source of manganese in the
United States (Arkansas, Virginia, Georgia); also in India, South Africa,
and Russia. CF:cryptomelane; wad.
b. See:romanechite; manganese oxide. CF:pyrolusite
See:psilomelane