franklinite : List Of Minerals : The Stone Network
The Business To Business Portal For The Natural Stone Trade

Premium Black Galaxy Granite Slabs
Direct From The Factory
Ex-India

Mobile

Directory

Stone Fairs

Exhibitions 2017 Country
Exhibitions 2017 By Date

Stone Images

Granite
Limestone
Marble
Onyx
Quartzite
Sandstone
Slate
Travertine

Stone Machines

New Stone Machines
Used Stone Machines

Stone Sites

Stone Forums
Stone Magazines
Stone Portals

Stone Standards

CE Marking

Stone Supplies & Fabricators

Australia
Canada
United Kingdom
U.S.A.

Stone Testing

ASTM
BRE
Sandberg
Stats
Stone Initiatives
UKAS

Petrology

Granite
Limestone
Marble
Quartzite
Sandstone
Slate
Travertine

Rocks

Igneous
List of Minerals
List of Rocks
Metamorphic
Minerals
Sedimentary

Various Resources

A To Z Stone Names
Anti Slip
BIDA
Building Conservation
Building Design
English Heritage
Maintenance Products
Natural Stone Database
RIBA
RICS
Salvo
SPAB
Stone Federation GB
Trade Terminology

The spinels are any of a class of minerals which crystallize in the isometric system with an octahedral habit. The general formula is as (X)(Y)2O4, with X representing cations occupying tetrahedral sites and Y cations occupying octahedral sites. Divalent, trivalent, and quadrivalent cations can occupy the X and Y sites, and they include magnesium, zinc, iron, manganese, aluminium, chromium, titanium, and silicon.

The oxygen anions are arranged in a cubic close-packed structure. In the normal spinel structure, X cations occupy the tetrahedral sites, and Y the octahedral sites. For inverse spinels, half the Y cations occupy the tetrahedral sites, and both X and Y cations occupy the octahedral sites.

Important members of the spinel group include:

Spinel – MgAl2O4, after which this class of minerals is named

Gahnite - ZnAl2O4

Franklinite - (Fe,Mn,Zn)(Fe,Mn)2O4

Chromite - (Fe·Mg)Cr2O4

Magnetite - Fe3O4

Hercynite - FeAl2O4

Ulvöspinel - TiFe2O4

Jacobsite - MnFe2O4

Trevorite - NiFe2O4

Ringwoodite - SiMg2O4, an abundant olivine polymorph within the Earth's mantle from about 520 to 660 km depth, and a rare mineral in meteorites.

True spinel has long been found in the gemstone-bearing gravel of Sri Lanka and in limestones of Myanmar and Thailand.

Spinel usually occurs in isometric crystals, octahedrons, usually twinned. It has an imperfect octahedral cleavage and a conchoidal fracture. Its hardness is 8, its specific gravity is 3.5-4.1 and it is transparent to opaque with a vitreous to dull lustre. It may be colorless, but is usually various shades of red, blue, green, yellow, brown or black. There is a unique natural white spinel, now lost, that surfaced briefly in what is now Sri Lanka. Another famous spinel is the Black Prince's Ruby in the British Crown Jewels.

The transparent red spinels are called spinel-rubies or balas-rubies and were often confused with actual rubies in ancient times. "Balas" is derived from Balascia, the ancient name for Badakhshan, a region in central Asia situated in the upper valley of the Kokcha river, one of the principal tributaries of the Oxus river. Yellow spinel is called rubicelle and violet-colored manganese-bearing spinel is called almandine.

Spinel is found as a metamorphic mineral, and also as a primary mineral in basic rocks, because in such magmas the absence of alkalis prevents the formation of feldspars and any aluminium oxide present will form corundum or combine with magnesia to form spinel. This is why spinel and ruby are often found together.

Spinel, (Mg,Fe)(Al,Cr)2O4, is common in peridotite in the uppermost Earth's mantle, between the Mohorovicic discontinuity (the Moho) and a depth of 70 kilometers or so; below that depth, the spinel (if present) becomes increasingly rich in chromium, as with increasing depth, pyrope-rich garnet becomes the more stable aluminous mineral in peridotite. At depths significantly shallower than the Moho, calcic plagioclase is the more stable aluminous mineral in peridotite.

  • Mexican Black Spinel
  • Known to the Aztec and ancient Mayan civilizations, Indian legends indicate that this gemstone was worn in battle for personal protection to ward off evil spirits and attract wealth to the stone bearer. Lost for centuries, the source of Mexican Black Spinel has been re-discovered in Mexico's Nayarit Province.

    Trade Supplies
    Information
    Information
  • Absolute Black Granite : Black Galaxy, Star Galaxy, Nero Impala etc. Black is popular, black looks great, black is more expensive >>>
  • Black Galaxy Granite : Quarrying & Quality Information >>>
  • M.I.A. Information
    Copyright :
    Legal Information
    This web site is protected under International Law by the
    Digital Millennium Copyright Act 1998.

    If you wish to link to this site please feel free to do so HOWEVER blatant design copying, code copying and theft of bandwidth will result in legal action!

    Digg Logo ImageDigg Facebook Logo ImageFacebook Reddit Logo ImageReddit StumbleUpon Logo ImageStumbleUpon Twitter Logo ImageTwitter

    Home : Contact : About : Legal : Privacy : Cookies : Copyright 1998-2017 : The Stone Network