a. A red-spotted, deep-green variety of chalcedony (cryptocrystalline
quartz) used as a semiprecious stone. Syn:bloodstone
b. An instrument used in geodetic surveying to aid in making long-distance
(as much as 320 km) observations; composed of one or more plane mirrors so
mounted and arranged that a beam of sunlight is reflected toward a distant
survey station where it is observed with a theodolite.
An inert, monatomic, colorless, odorless element, the lightest of the rare
gases. Except for hydrogen, helium is the most abundant element found in
the universe. The bulk of the world's supply is obtained from wells.
Symbol, He. Widely used in cryogenic research; vital in the study of
superconductivity. Helium is used for arc welding, as a cooling medium for
nuclear reactors, and as a gas for supersonic wind tunnels; extensively
used for filling balloons as it is much safer than hydrogen. One of the
recent largest uses for helium has been for pressuring liquid fuel
rockets. Handbook of Chemistry and Physics, 3
See:helicitic
a. Large detached crags; a confused pile or range of rocks. Arkell
b. Bare tracts of limestone. Arkell
A triclinic mineral, NiCO3 .6H2 O ; occurs with zaratite at
the Lord Brassey nickel mine, Heazlewood, Tasmania.
A pair of similar coaxial coils with their distance apart equal to their
radius, which permits an accurate calculation of the magnetic field
between the coils. Used in calibration of magnetometers. AGI
See:pig tailer
An isometric mineral, 2[Mn4 Be3 (SiO4 )3 S] ;
manganese may be replaced by iron toward danalite, or by Zn toward
genthelvite; forms tetrahedra; Mohs hardness, 6 to 6-1/2; in veins with
quartz, hornblende, and iron oxide; in pegmatites, and some alkaline
igneous rocks.
A brownish-red to garnet-red, transparent to translucent, hydrous
manganese arsenate, Mn3 (AsO4 )(OH)3 .H2 O ;
soon turns black; Mohs hardness, 3; sp gr, 3.50 to 3.65; rare; from
Nordmark, Sweden. Syn:aimafibrite
A copyrighted, confusing name for an imitation of hematite. Usually in the
form of an imitation cuvette. Apparently an artificially processed friable
mineral or other substance. Breaks easily. Mohs hardness, about 6.5; sp
gr, 4.8; streak, black.
a. A trigonal mineral, alpha -Fe2 O3 ; red if earthy,
reddish to bluish gray if massive, or bright metallic steel-gray in thin
tablets or micalike flakes (specular hematite); invariably has red ocher
streak. Kidney ore is massive reniform hematite. Commonly associated with
quartz, oxyhydroxides such as goethite or limonite, and magnetite, after
which it may be pseudomorphic; nonmagnetic when pure, but may appear
magnetic due to residual or included magnetite or maghemite; the most
widely mined ore of iron; in sedimentary rocks, Precambrian banded iron
formations (including their metamorphosed equivalents), oolitic
ironstones, contact-metamorphic deposits, commonly by alteration of
magnetite; may be of secondary origin, having formed by oxidation and
decomposition of iron silicates and carbonates; also occurs as a primary
mineral in veins and replacement deposits associated with igneous
intrusions, and in fumarolic deposits from volcanic gases.
See also:iron ore; specularite. Syn:specular iron ore; oligist;
oligist iron.
b. The mineral group corundum, eskolite, hematite, and karelianite.
See:itabirite
Any synthetic imitation of hematite.
A prefix meaning half.
See:hyalocrystalline
The upper or lower two faces of a dome resulting from symmetry lower than
that required for a dome in orthorhombic or monoclinic crystal systems.
In crystallography, having lower symmetry, resulting in forms with half
the number of faces as the holohedral point group. CF:holohedral;
merohedral.
In crystallography, having no transverse plane of symmetry and no center
of symmetry, and composed of forms belonging to only one end of the axis
of symmetry. Fay
In crystallography, refers to minerals in crystal classes with merohedral
symmetry such that crystal forms are different at opposite ends of the
crystallographic axes, thus permitting polar crystal properties; e.g.,
hemimorphite, zincite.
See:semiopal
Sharing neritic and pelagic qualities. AGI