Chlorastrolite (a variety of Pumpellyite-Mg)
Current inventory:  0 gems
 

  
Chlorastrolite is named from the Greek words meaning green star stone. Pumpellyite-(Mg) is named for Raphael Pumpelly (1837-1923), pioneer student of the paragenesis of copper deposit minerals of the Keweenaw Peninsula, Michigan, USA, and its dominant magnesium content.

Discovered in 1847;   IMA status: Not Valid (a variety of Pumpellyite-(Mg))

Chemistry

Chemical Formula:

Ca₂MgAl₂(SiO₄)(Si₂O₇)(OH)₂ • (H₂O)

Hydrated Calcium Magnesium Silicate Hydroxide

Molecular Weight:

470.70 gm

Composition:

Calcium

17.03 %

Ca

23.83 %

CaO

Magnesium

5.16 %

Mg

8.56 %

MgO

Aluminum

11.46 %

Al

21.66 %

Al₂O₃

Silicon

17.90 %

Si

38.29 %

SiO₂

Hydrogen

0.86 %

H

7.65 %

H₂O

Oxygen

47.39 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/C.24-30

Nickel-Strunz 10th Ed. ID:

9.BG.20

9 : SILICATES (Germanates)
B : Sorosilicates
G : Sorosilicates with mixed SiO₄ and Si₂O₇ groups; cations in octahedral [6] and greater coordination

Related to:

Pumpellyite Group. Pumpellyite-(Mg)-Pumpelleyite-(Fe²⁺) Series. Julgoldite-(Fe²⁺)-Pumpellyite-(Mg) Series.

Members of Group:

Pumpellyite Group: Julgoldite-(Fe²⁺), Julgoldite-(Fe³⁺), Julgoldite-(Mg), Okhotskite, Poppiite, Pumpellyite-(Al), Pumpellyite-(Fe²⁺), Pumpellyite-(Fe³⁺), Pumpellyite-(Mg), Pumpellyite-(Mg²⁺), Shuiskite

Varieties:

None

Synonyms:

Green Starstone, Greenstone, Isle Royale Greenstone, Lake Superior Greenstone, Turtleback

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

Crystals are fibrous, flattened plates in clusters or dense mats or random fibers.

Twinning:

Rarely

Physical Properties

Cleavage:

No cleavage in massive material

Fracture:

Splintery (massive material); Subconchoidal

Tenacity:

Brittle

Moh's Hardness:

5.0 - 6.0

Density:

3.10 - 3.50 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Green, Bluish Green, Greenish Black, Brown; Colorless, Green, Yellow, Brown in thin section.

Transparency:

Translucent, Opaque

Luster:

Vitreous (glassy)

Refractive Index:

1.674 - 1.722  Biaxial ( + ) and ( - )

Birefringence:

0.0140 - 0.0220

Dispersion:

Relatively Strong; r < v  (less commonly r > v)

Pleochroism:

Strong; X = nearly colorless to pale greenish yellow; Y = blue-green; Z = almost colorless to brownish yellow.

Occurances

Geological Setting:

In a wide variety of igneous and metamorphic rocks and environments. A widespread product of low-grade metamorphism of amygdaloidal basalts and diabases; in glaucophane schists and in graywackes.

Common Associations:

Chlorite, Epidote, Actinolite, Lawsonite, Glaucophane, Prehnite, Zeolites, Quartz

Common Impurities:

None

Type Locality:

Isle Royale National Park, Lake Superior, Keweenaw Co., Michigan, USA.

Year Discovered:

1847

View mineral photos:

Pumpellyite Mineral Photos and Locations

More Information

Mindat.org  (Chlorastrolite)
Mindat.org  (Pumpellyite-Mg)
Webmineral.com  (Pumpellyite-Mg)

Chlorastrolite, also known as Greenstone or Green Starstone, is a rare variety of Pumpellyite-(Mg) that was first discovered at Isle Royale, Lake Superior, Michigan, USA by C. T. Jackson and J. D. Whitney in 1847. Chlorastrolite was once thought to be an impure variety of Prehnite or Thomsonite. Beautiful dark green Chlorastrolie cabochons exhibit chatoyancy in a distinctive mosaic or segmented pattern sometimes referred to as "turtleback" due to its similarity to the pattern on a turtle shell. The colors of Chlorastrolite resemble fine Emerald or Imperial Jade. Chlorastrolite is the state gemstone of Michigan.
 

  
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