Mineral Information and Data:

Merwinite
Ca3Mg(SiO4)2 [CNMNC approved formula]

Named in honor of Herbert Eugene Merwin (1878-1963), American mineralogist and petrologist, Carnegie Institute, Washington, D.C., USA.

IMA status : Valid species (Pre-IMA 1921) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
51.04.02.01  
  (51) Nesosilicate Insular SiO4 Groups Only
  (51.04) with cations in [6] and >[6] coordination
  (51.04.02)
  
Nickel-Strunz
(10th edition) :
09.AD.15
  (09) Silicates
  (09.A) Nesosilicates (Isolated tetrahedron) structures
  (09.AD) Nesosilicates without additional anions; cations in [6] and/or greater coordination
  
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Space group: P21/a
Unit cell: a = 13.254(21)Å, b = 5.293(9)Å, c = 9.328(17)Å β = 91.90°, Z=4
Crystal Habit: Crystals are rare and inevitably pitted and rounded, to 3 mm; compact, massive.
Twinning: Polysynthetic on {100}, twin axis [013], common
  
Color: Colorless, white, very pale green; colorless in thin section
Diaphaneity: Transparent to translucent
Luster: Vitreous
Hardness (Mohs): 6
Measured Density: 3.15 - 3.32 g/cm3
Cleavage: Perfect on {100}
  
Geologic Setting: In siliceous dolomitic limestone in contact metamorphic zones, formed at relatively elevated temperatures, locally in substantial quantities.
Mineral Association: Gehlenite, spurrite, monticellite, vesuvianite (Crestmore, California, USA); spurrite, gehlenite, spinel (Scawt Hill, Ireland)
  

 

Merwinite
White masses of merwinite throughout the matrix
with minor blue calcite and plombierite.
Origin: Crestmore quarries, Crestmore, Riverside Co., California, U.S.A.
Sample size: 1.7 x 1 x 4.2 cm
Photo: Dan Weinrich

 

Merwinite
(zoom-in of above)

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