Pumpellyite

Pumpellyite is a group of closely related sorosilicate minerals:

• pumpellyite-(Mg): Ca₂MgAl₂[Si₂O₆OH][SiO₄](OH)₂(OH)^[4]
• pumpellyite-(Fe2+): Ca₂Fe²⁺Al₂[Si₂O₆OH][SiO₄](OH)₂(OH)^[5]
• pumpellyite-(Fe3+): Ca₂Fe³⁺Al₂[Si₂O₆OH][SiO₄](OH)₂O^[6]
• pumpellyite-(Mn2+): Ca₂Mn²⁺Al₂[Si₂O₆OH][SiO₄](OH)₂(OH)^[7]
• pumpellyite-(Al): Ca₂AlAl₂[Si₂O₆OH][SiO₄](OH)₂O^[8]

Pumpellyite
General
Category	Sorosilicate
IMA symbol	Pmp[1]
Strunz classification	9.BG.20
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	A2/m
Identification
Color	Olive green to bluish green
Cleavage	Good in two directions
Fracture	Uneven
Tenacity	Brittle
Mohs scale hardness	5.5-6
Luster	Vitreous, dull
Streak	White
Diaphaneity	Translucent
Specific gravity	3.2
References	[2] [3]

Pumpellyite crystallizes in the monoclinic-prismatic crystal system. It typically occurs as blue-green to olive green fibrous to lamellar masses. It is translucent and glassy with a Mohs hardness of 5.5 and a specific gravity of 3.2. It has refractive indices of n_α=1.674–1.748, n_β=1.675–1.754 and n_γ=1.688–1.764.

Pumpellyite occurs as amygdaloidal and fracture fillings in basaltic and gabbroic rocks in metamorphic terranes. It is an indicator mineral of the prehnite-pumpellyite metamorphic facies. It is associated with chlorite, epidote, quartz, calcite and prehnite.

It was first described in 1925 for occurrences in the Calumet mine, Houghton Co., Keweenaw Peninisula, Michigan, and named for United States geologist Raphael Pumpelly (1837–1923).^[9]

See also

• Chlorastrolite
• Dallasite