(Na,K)ThSi11(O,F,OH)25 · · 8H
Thornasite was described from Mont Saint-Hilaire in 1987. Its occurs extremely rarely and it fluoresces very bright green under SW and LW.
PHYSICAL CHARACTERISTICS:
Color is usually colorless or very pale green.
Luster is vitreous to silky, greasy or dull.
Diaphaneity is transparent to translucent.
Crystal System is hexagonal; 32.
Crystal Habits include embedded anhedral crystals and irregular
grains to 0.7mm.
Cleavage none observed.
Fracture is subconchoidal to uneven.
Hardness is not measured.
Specific Gravity is approximately 2.6 g/cm
Streak is white.
Associated Minerals include albite, analcime, calcite, catapleiite,
epididymite, eudialyte, leifite, mangan-neptunite, microcline,
natrolite, polylithionite, sérandite, steacyite and yofortierite.
Distinguishing Features: Color and mineral associations.
Origin: Named in 1987 for its composition; thorium, sodium and
silicon (Thor + Na + S + ite), formerly designated as UK #27.
CLASSIFICATION:
Dana System
# 72.1.2.1
Strunz Classification
# VIII/D.20-10
REFERENCES:
CanMin 25:181-183 (1987), MinRec 21:342-343 (1990),
Dana 8:1521-1522 (1997)
DISTRIBUTION AND RARITY AT MONT SAINT-HILAIRE:
MSH
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