Mineral Information and Data:

Barstowite
Pb4CO3Cl6 • H2O [CNMNC approved formula]

Named for Richard William Barstow (1947-1982), mineral collector and dealer of Cornwall, England.

IMA status : Approved Species 1991 (IMA1989-057)
CLASSIFICATION 
Dana
(8th edition) :
12.01.07.01  
  (12) Compound Halides
  (12.01) with miscellaneous anions
  (12.01.07)
  
Nickel-Strunz
(10th edition) :
03.DC.95
  (03) Halides
  (03.D) Oxyhalides, Hydroxyhalides and Related Double Halides
  (03.DC) With Pb (As,Sb,Bi), without Cu
  
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Space group: P21/m
Unit cell: a = 4.2043(8) Å, b = 9.199(2) Å, c = 16.663(3) Å β = 91.82(1)°
Crystal Habit: Crystals are elongated, to 2 cm, commonly in subparallel aggregates.
  
Color: Colorless to white; in reflected light shows abundant colorless internal reflections
Diaphaneity: Transparent to opaque
Luster: Adamantine
Hardness (Mohs): 3
Measured Density: 5.71(23) g/cm3
Cleavage: Prismatic, imperfect
Tenacity: Brittle
Fracture: Uneven
Streak: White
  
Geologic Setting: A rare reaction product of sea water with a metal-bearing vein exposed at sea level (Bounds Cliff, England); produced by the action of sea water on lead-bearing slag (Laurium, Greece; Baratti Beach, Italy); a corrosion product of lead object (Mahdia, Tunisia).
Mineral Association: Phosgenite, galena, jamesonite, cerussite, pyrite, sphalerite, chalcopyrite, dolomite, quartz (Bounds Cliff, England)
  

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