Spinel Group Flashcards
MgAl2O4
Spinel
Isometric. Commonly in octahedral crystals or in twinned octahedrons (spinel twins). Dodecahedron may be present as small truncations but other forms are rare.
Spinel
Hardness of spinel?
8
Specific gravity of spinel?
3.5-4.1
What is the usual color of spinel?
Various shades of white, red, lavender, blue, green, brown, and black.
A common high-temperature mineral occurring in contact-metamorphosed limestones and metamorphic rocks poor in SiO2. Metamorphic assemblages may contain phlogopite, pyrrhotite, and graphite.
Spinel
Fe3O4
Magnetite
Isometric. Frequently in octahedral crystals, more rarely in dodecahedrons. Other forms rare.
Magnetite
What is the cleavage of magnetite?
None. Octahedral parting in some specimens.
What is the hardness of magnetite?
6
What is the specific gravity of magnetite?
5.18
What is the usual color of magnetite?
Iron black. Luster metallic.
Magnetite may act as a natural magnet known as ______.
lodestone
Common mineral found disseminated as an accessory in most igneous rocks. In some igneous rock types magnetite may be the chief constituent of the rock and may form large ore zones; these are commonly titaniferous.
occurrence of magnetite
Magnetite may be closely intergrown with corundum, forming ______.
emery
FeCr2O4
Chromite
Isometric, with octahedral habit, but crystals rare. Commonly massive, granular to compact.
crystal form of chromite
What is the hardness of chromite?
5 1/2
What is the specific gravity of chromite?
4.6
What is the usual color of chromite?
Iron black to brownish black
A common constituent of peridotites, of other ultrabasic rocks, and of serpentine derived from them. Associated with olivine, serpentine, and corundum.
Chromite
