SPINEL[GEM]

LISTING DESCRIPTION
Spinel is the magnesium aluminium member of the larger spinel group of minerals. It has the formula MgAl2O4.[1] Balas ruby is an old name for a rose-tinted variety.
Spinel group
The spinels are any of a class of minerals of general formulation A2+B23+O42- which crystallise in the cubic (isometric) crystal system, with the oxide anions arranged in a cubic close-packed lattice and the cations A and B occupying some or all of the octahedral and tetrahedral sites in the lattice.

DETAILED DESACRIPTION

Spinel is the magnesium aluminium member of the larger spinel group of minerals. It has the formula MgAl2O4.[1] Balas ruby is an old name for a rose-tinted variety.
Spinel group
The spinels are any of a class of minerals of general formulation A2+B23+O42- which crystallise in the cubic (isometric) crystal system, with the oxide anions arranged in a cubic close-packed lattice and the cations A and B occupying some or all of the octahedral and tetrahedral sites in the lattice. A and B can be divalent, trivalent, or quadrivalent cations, including magnesium, zinc, iron, manganese, aluminium, chromium, titanium, and silicon. Although the anion is normally oxide, structures are also known for the rest of the chalcogenides. A and B can also be the same metal under different charges, such as the case in Fe3O4 (as Fe2+Fe23+O42-).
Members of the spinel group include:[3]
Properties of true spinel
Spinel crystallizes in the isometric system; common crystal forms are octahedra, 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 luster. 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. Some spinels are among the most famous gemstones: Among them is the Black Prince's Ruby and the 'Timur ruby' in the British Crown Jewels, and the 'cote de Bretagne' formerly from the French Crown jewels. The Samarian Spinel is the largest known spinel in the world, weighing 500 carats (100 g).
The transparent red spinels were called spinel-rubies or balas rubies. In the past, before the arrival of modern science, spinels and rubies were equally known as rubies. After the 18th century the word ruby was only used for the red gem variety of the mineral corundum and the word spinel became used. "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. The Badakshan Province was for centuries the main source for red and pink spinels.
Occurrence
True spinel has long been found in the gemstone-bearing gravel of Sri Lanka and in limestones of the Badakshan Province in nowadays Afghanistan and of Mogok in Burma. Recently gem quality spinels were also found in the marbles of Luc Yen (Vietnam), Mahenge and Matombo (Tanzania), Tsavo (Kenya) and in the gravels of Tunduru (Tanzania) and Ilakaka (Madagascar). Spinel is found as a metamorphic mineral, and also as a primary mineral in rare mafic igneous rocks; in these igneous rocks, the magmas are relatively deficient in alkalis relative to aluminium, and aluminium oxide may form as the mineral corundum or may 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 450 km (where olivine is metamorphosed to spinel) to 670 km kilometers or so; below that depth, the spinel is oxidised. At depths significantly shallower than the Moho, calcic plagioclase is the more stable aluminous mineral in peridotite.
Spinel, (Mg,Fe)Al2O4, is a common mineral in the Ca-Al-rich inclusions (CAIs) in some chondritic meteorites.
The spinel structure
Normal spinel structures are usually cubic closed-packed oxides with one octahedral and two tetrahedral sites per oxide. The tetrahedral points are smaller than the octahedral points. B3+ ions occupy the octahedral holes because of a charge factor, but can only occupy half of the octahedral holes. A2+ ions occupy 1/8th of the tetrahedral holes. This maximises the lattice energy if the ions are similar in size. A common example of a normal spinel is MgAl2O4.
Inverse spinel structures however are slightly different in that one must take into account the crystal field stabilization energies (CFSE) of the transition metals present. Some ions may have a distinct preference on the octahedral site which is dependent on the d-electron count. If the A2+ ions have a strong preference for the octahedral site, they will force their way into it and displace half of the B3+ ions from the octahedral sites to the tetrahedral sites. If the B3+ ions have a low or zero octahedral site stabilization energy (OSSE), then they have no preference and will adopt the tetrahedral site. A common example of an inverse spinel is Fe3O4, if the Fe2+ (A2+) ions are d6 high-spin and the Fe3+ (B3+) ions are d5 high-spin.
For many years, crystal field theory was invoked to explain the distribution of the cations within the spinels. As the octahedral and tetrahedral sites in the lattice generate different amounts of CFSE, it was argued that the arrangement of the two types of cation that generated the most CFSE would be the most stable. However, this idea was challenged by Burdett and co-workers, who showed that a better treatment used the relative sizes of the s and p atomic orbitals of the two types of atom to determine their site preference.[4] This is because the dominant stabilizing interaction in the solids is not the crystal field stabilization energy generated by the interaction of the ligands with the d-electrons, but the σ-type interactions between the metal cations and the oxide anions. This rationale can explain anomalies in the spinel structures that crystal-field theory cannot, such as the marked preference of Al3+ cations for octahedral sites or of Zn2+ for tetrahedral sites - using crystal field theory would predict that both have no site preference. Only in cases where this size-based approach indicates no preference for one structure over another do crystal field effects make any difference — in effect they are just a small perturbation that can sometimes make a difference, but which often do not.
Synthetic spinel
Synthetic spinel was accidentally produced in the middle of the 18th century, and has been more recently described in scientific publications in 2000 and 2004.

Price
$39916096/kg or $18143680/ib

For more information:

mobile: +2348039721941

contact person: emeaba uche

e-mail: emeabau@yahoo.com

website: www.franchiseminerals.com



Comments

Post a Comment

Popular posts from this blog

AGATE[GEM]

Image
Listing description Agate (pronounced /ˈæ ɡə t/ ) is a microcrystalline variety of quartz ( silica ), chiefly chalcedony , characterised by its fineness of grain and brightness of color. Although agates may be found in various kinds of rock, they are classically associated with volcanic rocks but can be common in certain metamorphic rocks . [1] Detailed description Etymology and history The stone was given its name by Theophrastus , a Greek philosopher and naturalist, who discovered the stone along the shore line of the river Achates ( Greek : Ἀχάτης ) sometime between the 4th and 3rd centuries BC. [2] Colorful agates and other chalcedonies were obtained over 3,000 years ago from the Achates River, now called Dirillo , in Sicily . [3] Ancient use Agate is one of the most common materials used in the art of hardstone carving , and has been recovered at a number of ancient sites, indicating its widespread use in the ancient world; for example, archaeological recovery a...
Read more

ALEXANDRITE

Image
The alexandrite variety displays a color change ( alexandrite effect ) dependent upon the nature of ambient lighting. This color shift is independent of any change of hue with viewing direction through the crystal that would arise from pleochroism . Both these different properties are frequently referred to as "color change", however. DETAILED DESCRIPTION The alexandrite variety displays a color change ( alexandrite effect ) dependent upon the nature of ambient lighting. This color shift is independent of any change of hue with viewing direction through the crystal that would arise from pleochroism . Both these different properties are frequently referred to as "color change", however. Alexandrite results from small scale replacement of aluminium by chromium ions in the crystal structure, which causes intense absorption of light over a narrow range of wavelengths in the yellow region of the spectrum. Alexandrite from the Ural Mountains in Russia is gree...
Read more

TOURMALINE(RUBELITA)GEM

Image
Listing description : MINERALOGY:  The  pink tourmaline , also known as rubelita originates primarily in plutonitas acids, specifically  pegmatite , where forms large  crystals . Through the action of gases containing  boron, from the magma of the host rock, tourmaline it can also arise as inclusion neumatolítica  ( generated depth of the crust (Plutonism) by intrusion of magma, which causes alteration in petrographic composition of the invaded rocks ) then the crystals are included heavily on rock, the  pink tourmaline  consists of different mineral elements, but always has the same structure, the metals are always included in tourmalines and are causing varieties this mineral colors,  the pink tourmaline carries traces of manganese  that is what gives her cute pink. Detailed Description: MYTHOLOGY:  It was found in the Minas Gerais (Brazil)  crystal pink tourmaline (rubellite) of 109 cm.  pink tour...
Read more