Montmorillonite
(Na,Ca_0.5)_0.33(Al,Mg)₂Si₄O₁₀(OH)₂ · nH₂O

     Montmorillonite, a member of the smectite group, is very rare at Mont Saint-Hilaire.

PHYSICAL CHARACTERISTICS:

Color is usually white to tan.
Luster is earthy.
Diaphaneity is transparent to translucent.
Crystal System is monoclinic; C2/m.
Crystal Habits include compact powdery fillings.
Cleavage {001} is perfect (not seen in powdery material).
Fracture is absent due to clay-like nature.
Hardness is 1 -2.
Specific Gravity is approximately 2.7 g/cm³.
Streak is white.
Associated Minerals include albite and fluorite.
Distinguishing Features: none amongst other powdery material.
Origin: Named in 1847 after its discovery locality, at Montmorillon,
   northwest of Limoges, France.

CLASSIFICATION:

REFERENCES:
MinRec 21:323 (1990), Dana 8:1483-1485 (1997)

DISTRIBUTION AND RARITY AT MONT SAINT-HILAIRE:

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