| Chrome chalcedony | |
|---|---|
 Zimbabwean chrome chalcedony (known locally as mtorolite). Scale is in centimetres. | |
| General | |
| Category | Tectosilicate minerals |
| Group | Quartz group |
| Variety of | Chalcedony |
| Formula | Silica (SiO2) |
| Crystal system | Trigonal (quartz),monoclinic (moganite)[1] |
| Identification | |
| Formula mass | 60 g/mol |
| Color | Emerald green |
| Cleavage | Absent[2] |
| Fracture | Uneven, splintery, conchoidal[2] |
| Mohs scale hardness | 6–7[2] |
| Luster | Vitreous, dull, greasy, silky[2] |
| Streak | White |
| Diaphaneity | Translucent[2] |
| Specific gravity | Usually 2.60, sometimes greater than 2.62[3] |
Chrome chalcedony is agreen variety of themineralchalcedony, colored by small quantities ofchromium.[4]Its name is derived from Mutorashanga, a small ferrochrome mining town in Zimbabwe where the mineral was discovered in the 1950s.[5]
It is most commonly found inZimbabwe, where it is known asMtorolite,[6]Mtorodite,[7] orMatorolite.[8] It is also marketed using the trade name, Aquaprase.
Chrome chalcedony is similar in appearance to the better knownchrysoprase, but differs in that whilst chrome chalcedony is colored by chromium (aschromium(III) oxide), chrysoprase is colored bynickel.[4] The two can be distinguished with aChelsea color filter, as chrome chalcedony will appear red, whilst chrysoprase will appear green.[4][9] Chrome chalcedony (unlike chrysoprase) may also contain tiny black specks ofchromite.[3]
Chrome chalcedony is (together withagate,carnelian,chrysoprase,heliotrope,onyx and others) a variety ofchalcedony. This is acryptocrystalline form ofsilica, consisting of fine intergrowths of the mineralsquartz andmoganite.[1]
Chrome chalcedony (known as mtorolite, mtorodite or matorolite) occurs inZimbabwe, principally near to the mining town ofMtoroshanga, located on theGreat Dyke geological feature.[6] It has also been discovered in westernAustralia, theBalkans,Bolivia,Turkey and theUral Mountains.[10]
Chrome chalcedony was widely used injewellery andseals throughout theRoman Empire. The source of the mineral is unclear, as whilstPliny the Elder described it as coming fromIndia, no deposits have been found there. It may have come fromAnatolia (in modern-dayTurkey), where deposits are known to exist.[10]
Chrome chalcedony disappeared from use sometime in the 2nd century. It was only rediscovered when the Zimbabwean deposits were found in the 1950s.[11]
{{cite book}}: CS1 maint: postscript (link)| Crystalline | |||||||||
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| Cryptocrystalline | |||||||||
| Amorphous | |||||||||
| Miscellaneous | |||||||||
| Notable varieties |
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