a. A group name for distinctly crystalline forms of chlorite (such as
clinochlore and penninite).
b. A group name for chlorites conforming to the general formula: (R (super
2+) ,R3+ )6 (Si,Al)4 O10 (OH)8 .
A monoclinic mineral, KAlSi3 O8 ; feldspar group; prismatic
cleavage; partly ordered, monoclinic potassium feldspar dimorphous with
microcline, being stable at higher temperatures; also a general term
applied to any potassium feldspar that is or appears to be monoclinic;
e.g., sanidine, submicroscopically twinned microcline, adularia, and
twinned analbite. It is a common rock-forming mineral and occurs esp. in
granites, granite pegmatites, felsic igneous rocks, and crystalline
schists, and is commonly perthitic. Syn:common feldspar; orthose;
pegmatolite. CF:microcline; plagioclase; anorthoclase.
A descriptive name for rocks now known as monzonite, in which the
plagioclase is at least as calcic as labradorite. Holmes, 2
An orthoclase-bearing porphyritic intrusive rock, such as granite or
syenite. The term is sometimes restricted to rocks containing more than
90% orthoclase. Not recommended usage. AGI
Cleaving in directions at right angles to each other. Webster 3rd
a. A primary dolomite, or one formed by sedimentation. AGI
b. A term used by Tieje (1921) for a dolomite rock so well-cemented that
the particles are interlocking. AGI
A monoclinic crystal form whose faces parallel the orthoaxis and cut the
other axes. CF:dome; clinodome. AGI
An orthorhombic mineral, (Fe,Mg)2 Si2 O 6 ; pyroxene
group; now simply called ferrosilite. CF:ferrosilite; clinoferrosilite.
Applied to gneissose rocks that have been derived from rocks of igneous
origin. CF:paragneiss
At right angles. Hammond
Cesaro's name for an orthorhombic form of guarinite, through superposition
of hemitropic lamellae of the monoclinic mineral, clinoguarinite.
See also:clinoguarinite
Maceral having a normal hydrogen content, such as vitrine.
Tomkeieff
An artificial orthorhombic high-temperature polymorph of KAlSiO4 .
A term proposed by Brooks (1954) for sedimentary limestone.
CF:metalimestone; orthomarble. AGI
Applied to the main stage of crystallization of silicates from a typical
magma; the stage during which perhaps 90% of the magma crystallizes.
CF:pegmatitic stage
A crystalline limestone that will take a polish; e.g., the Holston
orthomarble of Tennessee. CF:metamarble; metalimestone; ortholimestone.
Triclinic feldspar, which by repeated twinning (orthomimicry) simulates a
higher degree of symmetry with rectangular cleavages; e.g., orthoclase,
anorthoclase, and cryptoclase. English
The product of a procedure that corrects the distortions in aerial
photography due to the instability of the camera platform, the terrain
relief, and the angle of the light rays entering the camera lens. The
ortho instrumentation attached to a stereo plotting instrument rectifies
the image in a transfer process so as to reposition it in its correct
planar position. SME, 1
Said of the texture of the groundmass in certain holocrystalline,
porphyritic, igneous rocks in which the feldspar crystals have quadratic
or short, stumpy, rectangular cross sections, rather than the lath-shaped
outline observed in trachytic texture. Also, said of a groundmass with
this texture, or of a rock having an orthophyric groundmass. AGI
In the monoclinic system, the form consisting of two planes parallel to
the vertical and orthodiagonal axes. See also:pinacoid
Standard, 2