Images
Formula: Ca(Si6Al2)O16.4H2O
Hydrated tectosilicate (framework silicate), zeolite group
Crystal system: Monoclinic
Specific gravity: 2.20 to 2.23 measured, 2.26 calculated
Hardness: 4½ to 5
Streak: White
Colour: Colourless, white, pinkish
Luminescence:
Solubility: Not attacked by hot or cold hydrochloric acid
Electrical: Piezoelectric and pyroelectric
Common impurities: Fe,Mg,Na,K
Environments
Metamorphic environments
Hot springs
Yugawaralite occurs as crystals lining cavities, and veinlets, typically deposited in active geothermal areas.
Associated minerals include zeolites,
gyrolite, okenite,
prehnite, quartz and
calcite
(HOM).
Localities
At the type locality, the Yugawara Hot Spring, Yugawara, Ashigarashimo District, Kanagawa Prefecture, Japan,
yugawaralite occurs in networks and veins and as crystals in cavities in
andesite tuffs that have
been altered by waters of hot springs. The locality is 300 m from the hot spring. Yugawaralite is colourless
to white, with a vitreous lustre, and one commonly iridescent
(AM 38.426-426).
Associated minerals include chabazite,
laumontite and quartz
(Mindat).
Yugawaralite from the Yugawara Hot Spring -
Image
At Osilo, Sassari Province, Sardinia, Italy, a sample was collected from an outcrop on the slope of Mt. Crastu Muradu.
The rock is an altered, grey-green trachyandesite that has
numerous cavities and fractures filled with variable amounts of yugawaralite,
laumonite, heulandite,
stilbite, chabazite,
epistilbite, heulandite,
mordenite, baryte,
calcite, ankerite and
quartz. All yugawaralite extends from a substrate of well crystallised
calcite and is associated with
laumontite, heulandite and
stilbite. Yugawaralite has been found with
mordenite in only one geode, and has not been found with
chabazite.
Yugawaralite occurs as parallel aggregates of well formed, clear white, tabular crystals set on a matrix of
scalenohedral calcite
(CM 15.1.113-114).
Yugawaralite from Osilo - Image
At the Chena Hot Springs (yugawaralite locality), Tors Campground Trail, Chena River, Fairbanks North Star Borough,
Alaska, USA, the upland is underlain by complexly folded and faulted
schist, gneiss,
quartzite, phyllite,
slate and metachert
which have been intruded by granitic rocks.
Yugawaralite, associated with quartz,
laumontite, stellerite and
stilbite, occurs mainly in a siliceous xenolith near the edge of a small
porphyritic quartz
monzonite pluton. The host rock of the yugawaralite is
brecciated, sugary-textured
metachert, or very fine-grained
quartzite that is veined with
quartz, chalcedony and minor
opal. At joint intersections,
quartz-encrusted yugawaralite crystals, up to 8 mm long, coat joint
surfaces and vug-like enlargements. Locally, fractures are completely filled with yugawaralite,
quartz, stellerite,
stilbite and laumontite. A film
of hydrous iron oxide coats quartz and the surface of many yugawaralite
crystals. Crystals of stellerite and
stilbite are closely associated with the yugawaralite. A soft white
powdery coating of laumontite commonly occurs on crystals of
yugawaralite, stellerite,
stilbite and quartz in the vugs.
The quartz monzonite
contains plagioclase, quartz,
K-feldspar and minor biotite;
accessory minerals are zircon,
allanite, greenish-brown
tourmaline and cerite. The
K-feldspar occurs as xenomorphic phenocrysts, up to 1.5 cm across, that
enclose the other minerals.
The fact that the Alaska occurrence is only 14 miles from Chena Hot springs suggest the possibility of a similar
geothermal origin. There is, however, no evidence of past or present thermal spring activity at the yugawaralite
locality. Furthermore, the Chena Hot Springs are dilute thermal waters of probable meteoric origin that contain
considerable silica and sulphate ions, but little calcium and magnesium. Very little mineral deposition is now taking
place at Chena Hot Springs
(AM 56.1699-1717).
Yugawaralite from the Chena Hot Springs deposit
- Image
Back to Minerals