Collector quality gemstone! This 3.30 CT Octagon Natural Gahnite is very rare. It throws such sparkle when rotated in the light. Very flashy. The Octagon cut is also very unusual. This would be good for collectors of fine gems. It is a beautiful green-blue color. Comes with a certificate/gem identification card with a photo of the stone. from AGSL Gem Security Laboratory. Measures: 8.88 x 8.48 x 5.79 mm. Refractive Index: 1.79 - 1.80. Specific Gravity: 4.38 - 4.60. Origin: Delama. Hardness: 7.5 - 8 Mohs. More info; Gahnite Rare Mineral Gahnite, ZnAl₂O₄, is a rare mineral belonging to the spinel group. It forms octahedral crystals which may be green, blue, yellow, brown or grey. It often forms as an alteration product of sphalerite in altered massive sulphide deposits such as at Broken Hill, Australia. Other occurrences include Falun, Sweden where it is found in pegmatites and skarns, Charlemont, Massachusetts; Spruce Pine, North Carolina; White Picacho district, Arizona; Topsham, Maine; and Franklin, New Jersey in the United States. source: Wikipedia Chemical formula: ZnAl₂O₄