Zeolites: Lomontite
Diagnostic card.
Ca (Al, Si2O6) 2 * 4H2O
Singonia monoclinic
Hardness 3-3,5
Specific weight 2.2-2.35
Cleavage is perfect
Crack irregular
Color is colorless, differently colored
Color in powder white
Glitter from glass to pearly
Crystallizes in the form of prismatic crystals, elongated and fibrous. Coloration light gray or yellowish, glossy glass with a tendency to pearly.
Singonia, symmetry class, space group. Monoclinic; 2 or m; C2 or Cm, respectively. Habit. Occurs in the form of crystals; Typical are small prismatic crystals with a beveled end; Also massive. Doubles. Usually by {100}. Cleavage. By {010}, {110} is perfect. Other properties. Lomontite is a strong pyroelectric (its crystals do not have a center of symmetry). Changes. Lomontite easily loses about 1/8 of the water, becoming opaque and brittle (a variant - leongardite).
Diagnostic signs.
The shape of the crystals and the nature of the change. In hydrochloric acid dissolves, releasing jelly-like silica. In the flame of the candle it is easy to melt. In HCl lomontite forms a gelatinous precipitate. With moderate heating or under the influence of dry air, loses water, turning into leongardite - an opaque, crumbling, partially degregrated variety of lomontite. Most of the samples in the collections are actually represented by leongardite.
Origin.
Lomontite is found in igneous rocks as acidic (granites and pegmatites), and basic (basalts and diabases) composition. It also fills cracks in metamorphic rocks, set in ore-bearing hydrothermal veins.
Place of Birth.
Beautiful crystalline forms occur in the form of druses in granites and pegmatites of the eastern Pyrenees, in the void of effusive rocks of New Zealand, in the quartzite of the Ardenna Plateau, in the cornubianites of southern Norway, in the diabases of New Jersey (USA) and in the basaltic rocks of Poona (India). Magnificent crystals were also observed in Italy in the granites of Baveno near Lake Lago-Major.
Lomontite (alpha-leongardite). Украинка с. (= Former Kurchi), okr-t of Simferopol, Crimea, Ukraine. ~ 6x8 cm. Photo: © А.А. Evseev.
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