Barstowite Mineral Data

General Barstowite Information

Chemical Formula: Pb4(CO3)Cl6•(H2O) Composition: Molecular Weight = 1,119.54 gm    Hydrogen   0.18 %  H     1.61 % H₂O    Lead      74.03 %  Pb   79.75 % PbO    Carbon     1.07 %  C     3.93 % CO₂    Chlorine  19.00 %  Cl   19.00 % Cl                -   %   Cl   -4.29 % -O=Cl₂       Oxygen     5.72 %  O             ______        ______              100.00 %      100.00 % = TOTAL OXIDE Empirical Formula: Pb₄(CO₃)Cl₆•(H₂O) Environment: Quartz-dolomite ore vein exposed to sea water at the base of the cliff. IMA Status: Approved IMA 1991 Locality: Bounds Cliff, St. Endellion, Cornwall, England. Link to MinDat.org Location Data. Name Origin: Named for Richard William Barstow (1947-1982), Cornish mineral dealer. Name Pronunciation: Barstowite + Pronunciation Synonym: ICSD 411366   IMA1989-057   PDF 51-1520  

Barstowite Image

Images:

Barstowite Comments: SEM images of irregular prismatic barstowite with phosgenite. (MinMag, v55:378). Location: Lead-antimony vein at the southwestern end of Bounds Cliff, St Endellion, Cornwall, UK. Scale: Scale bar left 400 µm right 100 µm. © Mineralogical Magazine

Barstowite Crystallography

Axial Ratios: a:b:c =0.457:1:1.8113 Cell Dimensions: a = 4.2043, b = 9.199, c = 16.663, Z = 2; beta = 91.82° V = 644.12 Den(Calc)= 5.77 Crystal System: Monoclinic - PrismaticH-M Symbol (2/m) Space Group: P 2₁/m X Ray Diffraction: By Intensity(I/I_o): 4.02(1), 2.296(0.8), 2.377(0.6), Crystal Structure:

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Steele I M , Pluth J J , Stanley C J , Mineralogical Magazine , 63 (1999) p.901-907, Crystal structure of barstowite (3PbCl2PbCO3H2O), Locality: Bounds Cliff, St Endellion, Cornwall

 

Physical Properties of Barstowite

Cleavage: {???} Indistinct Color: Colorless, White. Density: 5.5 - 5.69, Average = 5.59 Diaphaneity: Transparent to Opaque Fracture: Brittle - Uneven - Very brittle fracture producing uneven fragments. Habit: Microscopic Crystals - Crystals visible only with microscopes. Habit: Prismatic - Crystals Shaped like Slender Prisms (e.g. tourmaline). Hardness: 3 - Calcite Luster: Adamantine Streak: white  

Optical Properties of Barstowite

Optical Data: Biaxial (?)   NCalc= 2.04 - from Gladstone-Dale relationship (KC = 0.1799) where Ncalc=Dcalc*KC+1
NCalc= 2.01 - from Gladstone-Dale relationship (KC = 0.1799) where Ncalc=Dmeas*KC+1 RL Anisotrophism: Weak to moderate. RL Bireflectance: Moderate, gray to dark gray. RL Color: White with abundant colorless internal reflections. Reflectivity Standardized Intensity (100%) Reflection Spectra of Barstowite in Air

λ	R1	R2		∑ R1(λ)	∑ R2(λ)
400 nm	14.20	14.80

     420 nm   14.00   14.60 
 440 nm   13.80   14.40 
 460 nm   13.70   14.10 
 480 nm   13.40   13.90 
 500 nm   13.20   13.70 
 520 nm   13.10   13.50 
 540 nm   12.90   13.40 
 560 nm   12.80   13.20 
 580 nm   12.70   13.10 
 600 nm   12.60   13.00 
 620 nm   12.50   12.90 
 640 nm   12.50   12.90 
 660 nm   12.40   12.80 
 680 nm   12.30   12.80 
 700 nm   12.30   12.70