26mm 18.85ct Hemimorphite cabochon

Item Information

Dimensions (mm) 26 x 18 x 5mm
Weight (carats) 18.85 carats


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We managed to find some of this rare gemstone on our last buying trip and we couldn’t quite believe our luck. Grab it as we wont get it again!

Hemimorphite is a rare gem quality form of zinc silicate. Hemimorphite is very closely associated with Smithsonite, another rare collector’s gem. For many years, hemimorphite and smithsonite were both classed together another gemstone called calamine because of the similarity. In 1803 it was discovered to be two different minerals by mineralogist, James Smithson (of the Smithsonian Institute).
Hemimorphite is a zinc silicate, whilst smithsonite is a zinc carbonate; zinc silicate Hemimorphite is considered to be rarer than Smithsonite. . The name ‘hemimorphite’ originates from the Greek words ‘hemi’ and ‘morph’, which respectively translate as ‘half-shape’. The name refers to its unusual hemimorphic crystal form, which means that the axial ends of crystals are asymmetrical. One end of each crystal is rather blunt, dominated by a pedion (a single face), while the other is pointed and pyramidal.
Hemimorphite can be identified by its distinct composition and unique crystal structure. Hemimorphite can be composed of over fifty percent zinc. Gemmologically, it has a refractive index of 1.614 to 1.636 and a density or specific gravity of 3.30 to 3.50. Its hardness is 5 on the Mohs scale.
Few deposits of Hemimorphite yield gemstone quality materials. Some of the most significant deposits are from Vieille Montagne, Belgium and Aachen, Germany, Mexico, Russia (Siberia), The Congo, Namibia, Madagascar and the United States, including Pennsylvania, Montana, Colorado and New Mexico.
Hemimorphite can occur in various tones of blue, green and colorless. Most gemstones are blue to blue-green, and look similar to chrysocolla or turquoise. The most desirable color is sky to Swiss blue, which is reminiscent of Paraiba tourmaline. Hemimorphite often exhibits bands of blue with white streaks, and it may also be found interspersed by a dark matrix. Gem quality hemimorphite typically ranges from transparent to translucent in clarity. There is no known treatment for this gemstone - it is natural and organic.

Chemical Formula: Zn4Si2O7(OH)2•H2O - Hydrous basic zinc silicate
Crystal Structure: Orthorhombic; tabular
Blue green, colorless
5 on the Mohs scale
Refractive Index:
1 614 to 1.636
3 30 to 3.50
Transparency Transparent to opaque
Double Refraction +0.022
Luster Vitreous, adamantine

Fluorescence: Weak

$99.95 USD

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Auction ID 637595
Watchers 9 watching
Viewed 1,425 times
Starts 22nd Feb 2017 3:16pm PST

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