Long mistaken for green peridot, Dunilite was identified in 2000 as a new gem variety from Olivine group. It is an orthorhombic, nagnesium, iron, magganese silicate. Through the x-ray diffraction pattern that line spacings are similar to peridot. These spacing, however, are not identical with those for peridot. By Dr. Mary L. Johnson, GIA July 8, 1998.
The color of dunilite varies from light greenish yellow to brownish green, the depth of color being related to the iron content. Dunilite is not quite as hard as quartz and thus is not one of the more durable of gems. It does not, however, have cleavage, and offers no problems for the lapidary.
Dunilite occurs in only one locality called "Katukubura mountain" Kolonne, Sri Lanka. It has been found as tabular rectangle shaped crystals in white Calcite rock. The first morphological data for dunilite was obtained from 0.97 carat faceted gemstone from GIA 10318180 Dated March 13, 1998 confirms the stone as a new member of the olivine group.
Faceted stones have a light greenish yellow appearance resembling, yellow chrysoberyl or sinhalite. The usual size range, is from 0.05 to one carat. Tiny faceted dunilite cut from the rough, transparent crystals. The largest Dunilite Olivine aggregate crystal weights 4.485 and a ferroedenite hornblende crystal 4.735 are now displayed in Natural History museum of Los Angeles county, 900 Exposition Boulevard, Los Angeles, California 9007, USA.
Few cabochon cut stones show 4 weak silver rays.
DUNILITE
Chemical Composition : Magnesium, iron, Manganese, Silicate
mpirical formula : (Mg1.53Fe0.48Mn 0.01)2.02 Si0.99 O4
Formula Contents on a basis of 4 anions.CaO : 0.09, MgO:38.87 MnO:0.31,
FeO:21.69, SiO2:37.61 Total:98.57wt%
Formula: (Mg, Fe, Mn)2 SiO2
Group : Olivine
Crystal System : Orthorhombic
Occurrence : In a huge white Calcite rock with black, amphibole rock.
Locality : Top, of Katukubura Mountain, Kolonne, Sri Lanka.
APPEARANCE AND PHYSICAL PROPERTIES
habit : Tabular, rectangle shaped aggregate crystals.
Color : Grey green crystals very small to large size.
Form : Prismatic with six sided rhombic crystal faces on corner. Not seen in other olivine crystals.
Color : Light Greenish Yellow
Lustre : Vitreous
Flourescence : None
Hardness : 6.5
Fracture : Uneven
Transparency : Transparent to Translucent
Cleavage : None
Specific gravity : 3.48 |
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