Formula: (Na2,Ca,K2)4(Al8Si40)O96·28H2O
From Alfredo Petrov:
MORDENITE (moruden-fusseki)
- Iwate: At Arasawa (Arasawa-mura), white transparent mordenite fibres to 5cm long, sometimes in cotton-like aggregates, fill amygdules in rhyolite-liparite. Some specimens are the most beautiful mordenites in Japan, as hemispherical sprays of silky white hairs to 5cm long, associated with minor quartz crystals. Microfibrous silky mordenite also composes much of a laminated or thinly bedded brownish white rock formed from altered volcanich ash.
- Kagoshima: With ginguro-type silver ore at the Tamanoyama mine. Small needles with dachiardite-Ca, heulandite and quartz in hydrothermal veins at the Onoyama gold mine. White to pink filiform crystals to 3mm, in reddish vesicular Pliocene hypabyssal rhyolite at Yoshida.
- Kanagawa: In altered andesite around Yugawara hot springs, filling amygdules with silky compact massive mordenite. In the Ohyama-Isehara district, and elsewhere in the eastern Tanzawa mountains, an upper zone of Miocene tuffs and volcanosedimentary rock, especially layers of glassy pumice tuff or glassy breccia, are altered to mordenite. Also in the Tanzawa mountains, with stilbite, heulandite and quartz in the outermost alteration zone around a quartz diorite (above the yugawaralite-bearing laumontite-wairakite zone).
- Miyagi: In the Katayama geothermal wells, Onikohbe, at depths of 140 metres, temperatures from 60 to 140 C, in altered Pliocene-Pleistocene andesitic and dacitic tuffs, above a laumontite-analcite-yugawaralite zone.
- Niigata: Beautiful crystals are found with clinoptilolite, erionite, chalcedony and quartz in vugs in mid-Miocene basaltic and dacitic agglomerate overlying olivine pillow basalt along the seashore at Maze. As cottony fibrous aggregates, associated with dachiardite-Na, clinoptilolite, barite and sulphides, in veins in altered rhyolite at Tsugawa. Drilling into marine strata in the Niigata oil field found mordenite with clinoptilolite at temperatures from 41 to 49 C.
- Shizuoka: Abundant as white fibrous tufts and filiform sprays to 1.5cm long in vugs, and as silky masses to 5cm, with calcite, celadonite, violet apophyllite, white chabazite and colourless heulandite, in altered volcanic agglomerates in cliffs and beach boulders around Shoubusawa and the neighboring Yanda coastal cliffs, both in Kawazu. Compact fibrous masses, surrounded by thick masses of blue-green celadonite, in agglomeratic andesite cliffs south of Shirahama (Shimoda city). Mordenite sprays are often embedded in solid calcite-filled vugs, but can be exposed with weak acids. Also at Toishinden, in veins cutting propylitized andesite. Also at Sotoura and Yazu.
- Tokyo: On Chichijima island: at Miyanohama, associated with pale yellow heulandite in andesite amygdules; at Hatsuneura, with dachiardite, heulandite and chalcedony; similarly at Susaki.
- Yamagata: In zeolitized tuff at Nagasawa.
- San-In district: abundant at Maji (Which prefecture???).
- N of Kanto (Which prefecture???): Motajuku district (similar to Kanagawa-ken’s Tanzawa zone around quartz diorite intrusion).
Above: Mordenite, Sotoura, Hatamachi, Shizuoka Prefecture, Japan. Flat lying acicular white sprays. Ex Allan and Elvire Mortimer. Ex I. Sunagawa. Measures 49x37x20mm.
