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 Home / Gem Library / Natural Gemstones / Gahnospinel July 19, 2019  

Natural Gahnospinel
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In 1937, gemologists B.W. Anderson and C.J. Payne reported the existence of a zinc-rich type of gem spinel that was transitional between spinel and gahnite and was rich in zinc. The name gahnospinel was then suggested for this species, which ranges from pale to dark blue and green.

Known Facts
Color Key: Dark Greenish, Dark Blue.
Refractive Index: 1.74 - 1.75
Chemical Composition: (Mg,Zn)Al2O4
Hardness: 8
Density: 4.1-4.40
Crystal Group: Cubic
Ocurrence: Tunduru, Tanzania; Ratanapura, Sri Lanka

Gahnospinel was originally reported from the gem gravels of Ratnapura in Sri Lanka. It is now known to also occur in the alluvial deposits from Tunduru, Tanzania albeit in very limited quantities. It looks like spinel, is singly refractive like spinel and falls within an identical color range. From appearance, its impossible to differentiate Gahnospinel from spinel but its specific gravity is somewhat higher.

From our investigations of mine run Tunduru spinels, the odds of finding a blue or a blue-green Gahnospinel seem to be in the order of something like one in ten thousand so these stones are quite rare. Black gahnospinel is either much more common or misidentified because it is being offered online from an undisclosed source in calibrated sizes.

Gahnospinel Gahnospinel
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Gahnospinel Stats/
Popularity Index: 4629hits
Total Items: 1items
Total Weight: CTS 1.46
Cheapest: USD 1359.00
Most Expensive: USD 1359.00
Largest: CTS 1.46
Smallest: CTS 1.46
Last Added: 05/26/17 10:31:52

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