Mineral Information and Data:

Bytownite
(Ca,Na)(Si,Al)4O8 [CNMNC approved formula]

Named in 1835 for the locality; Bytown (now Ottawa), Ontario, Canada.

IMA status : Intermediate Species Member; 2001 ()
CLASSIFICATION 
Dana
(8th edition) :
76.01.03.05  
  (76) Tectosilicate Al-Si Framework
  (76.01) with Al-Si frameworks
  (76.01.03) Plagioclase series
  
Nickel-Strunz
(10th edition) :
09.FA.35
  (09) Silicates
  (09.F) Tektosilicates without Zeolitic H2O
  (09.FA) Tektosilicates without additional non-tetrahedral anions
  
Crystal system: Triclinic System
Point group (H-M): 1 — pinacoidal
Unit cell: a = 8.18 Ǻ, b = 12.87 Ǻ, c = 14.19 Ǻ, α = 93.5°, β = 115.9°, γ = 90.6°
Crystal Habit: Crystals tabular; massive, granular
Twinning: Common by albite law; also by Carlsbad or pericline law
  
Color: Colorless, white, gray
Diaphaneity: Translucent to transparent
Luster: Vitreous, pearly on cleavages
Hardness (Mohs): 6 to 6.5
Measured Density: 2.72 to 2.74 g/cm3
Cleavage: 3; {001} perfect, {010} nearly perfect, {110} imperfect
Tenacity: Brittle
Fracture: Uneven to conchoidal
Streak: White
  
Geologic Setting: A rock-forming mineral typical of mafic intrusive igneous rocks, as gabbros and
anorthosites; as phenocrysts in basalts; rare in metamorphic rocks.
Mineral Association: Pyroxenes, olivine
  
Synonyms/varieties: Plagioclase [An 70-90]
Other Properties: Gemstone Extremely Rare.
Comments: Intermediate member of plagioclase series

 

Bytownite
Origin: Crystal Bay, Minesota, U.S.A.
Sample size: 4 x 5 cm
Photo: Diederik Visser

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