Chlorastrolite

Chlorastrolite is named from Greek "chloros" - green, and "astros" - star.

Chlorastrolite is often mottled light and dark green. The most desirable pattern resembles tortoiseshell. It is widely used in jewelry items that are not subjected to heavy wear.

Chlorastrolite is the state stone of Michigan, USA.
General Information
A variety or type of:Pumpellyite
Chemical Formula
Ca
 
2
(Mg,Fe)Al
 
2
(SiO
 
4
)(Si
 
2
O
 
7
)(OH)
 
2
· H
 
2
O)
Arthur Thomas, Gemstones (2009)
Photos of natural/un-cut material from mindat.org
Physical Properties of Chlorastrolite
Mohs Hardness5 to 6
Michael O’Donoghue, Gems, Sixth Edition (2006)
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Specific Gravity3.1 to 3.5
Michael O’Donoghue, Gems, Sixth Edition (2006)
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Cleavage QualityNone
Arthur Thomas, Gemstones (2009)
FractureSplintery
Arthur Thomas, Gemstones (2009) Granular
Optical Properties of Chlorastrolite
Refractive Index1.7
Michael O’Donoghue, Gems, Sixth Edition (2006)
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Birefringence0.010
Arthur Thomas, Gemstones (2009)
PleochroismNil
Arthur Thomas, Gemstones (2009)
DispersionNil
Arthur Thomas, Gemstones (2009)
Colour
Colour (General)Green and white patterns. The most desirable pattern resembles tortoiseshell.
Michael O’Donoghue, Gems, Sixth Edition (2006)
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Causes of ColourGreen, Fe2+-O-Fe3+ charge transfer coordination, plus Fe2+
W. William Hanneman, Pragmatic Spectroscopy For Gemologists (2011)
TransparencyOpaque
Michael O’Donoghue, Gems, Sixth Edition (2006)
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LustreSilky,Pearly
Arthur Thomas, Gemstones (2009)
Crystallography of Chlorastrolite
Crystal SystemOrthorhombic
Michael O’Donoghue, Gems, Sixth Edition (2006)
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HabitFibrous aggregates
Michael O’Donoghue, Gems, Sixth Edition (2006)
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Geological Environment
Where found:Occurs in cavities in amygdaloidal basalt tending to fill the smaller voids, few of which are larger than a pea.
Arthur Thomas, Gemstones (2009)
Further Information
Mineral information:Chlorastrolite information at mindat.org
Significant Gem Localities
USA
 
  • Michigan
    • Keweenaw Co.
      • Lake Superior
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