(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.
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.
CanMin 25:181-183 (1987), MinRec 21:342-343 (1990),
Dana 8:1521-1522 (1997)
DISTRIBUTION AND RARITY AT MONT SAINT-HILAIRE: