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Formula:
(Na2,Ca,K2)4(Al8Si40)O96.28H2O
Tectosilicate (framework silicate), zeolite group
Crystal System: Orthorhombic
Specific gravity: 2.12 to 2.15 measured, 2.125 calculated
Hardness: 4 to 5
Streak: White
Colour: Colourless, white, yellow, pink, orange, red
Common impurities: Mg
Environments:
Sedimentary environments
Hydrothermal environments
Basaltic cavities
Mordenite occurs in silica rich (eg rhyolitic) volcanics, in volcanic ash beds,
tuff, and rarely in
olivine - basalt. It is
of hydrothermal or sedimentary authigenic (formed in place) origin
(Dana.).
Associated minerals include zeolites,
calcite,
kaolinite and glauconite
(HOM).
Localities
The type locality is at Morden, Kings county, Nova Scotia, Canada.
At Glen Brittle, Minginish, Isle of Skye, Eilean á Chèo, Highland, Scotland, UK, plentiful good specimens of
mordenite occur in vesicular basaltic lava. Minor amounts of
other minerals are also present. Vesicles are abundant, and mordenite fills the overwhelming majority of
these vesicles, with other minerals present only in very subordinate amounts. The mordenite occurs as masses
composed of compact sprays of pure white radiating crystals up to 30 mm long, with a distinctive silky lustre, which
typically completely fill the vesicles. Other minerals found in the vesicles include
quartz, laumontite,
prehnite, calcite,
saponite and chabazite, although
prehnite and the single specimen of
chabazite found here are not associated with mordenite
(JRS 23.86-90).
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