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Formula: Ca(Al2Si3)O10.5-6H2O
Tectosilicate (framework silicate), zeolite group
Crystal system: Orthorhombic
Specific gravity: 2.14 measured, 2.05 calculated
Hardness: 5 to 5&~189;
Streak: White
Colour: Colourless, white
Luminescence:
Solubility:
Common impurities: Fe,Na,K+
Environments
Cowlesite occurs in cavities in basalts and
scoria, typically the only
zeolite within a single vesicle. Associated minerals include
zeolites and apophyllite
(HOM).
Localities
There are five co-type localities, Monte Lake, Kamloops Mining Division, British Columbia, Canada, an Unnamed wash,
adjacent to State Route 177, Superior area, Pinal County, Arizona, USA, North Table Mountain, Golden, Golden Mining
District, Jefferson County, Colorado, USA, Neer Road, Goble, Columbia County, Oregon, USA and Beech Creek Quarry,
Mount Vernon, Grant County, Oregon, USA.
At Monte Lake, Kamloops Mining Division, British Columbia, Canada, Samples of
basalt
scoria and breccias from
road cuts along logging roads south of the lake contain fairly abundant cowlesite. Although cowlesite
does not appear with any other zeolite in any single vug, other closely
associated zeolites are analcime,
thomsonite, ferrierite,
lévyne, stilbite,
heulandite and chabazite.
The cowlesite forms grey to blue-grey linings about 0.5 mm thick in vugs about 5 mm across. Many such linings
are globular from the merging of solid sprays of blades. lndividual crystals are small and not easily discernible
(AM 60.951-956).
Cowlesite from Monte Lake - Image
At an Unnamed wash, adjacent to State Route 177, Superior area, Pinal County, Arizona, USA, cowlesite fills tiny
vesicles in the outer margins of olivine
basalt bombs and scoria
fragments in an exhumed cinder cone. In the lower part of the cone cowlesite is abundant and closely associated
with thomsonite, chabazite,
analcime and calcite. Higher in the
exposure the main zeolites are
mordenite, thomsonite and
chabazite. The vesicles, about 1 mm across, are filled with white blades,
having grown radially inward. Larger vesicles contain compact balls of blades up to 1.5 mm across
(AM 60.951-956).
Cowlesite from the Unnamed wash - Image
At North Table Mountain, Golden, Golden Mining District, Jefferson County, Colorado, USA, Several specimens of
zeolite-bearing shoshonite
were found to contain small rosettes (about 1.5 mm across) and white blades with sharp terminations,
which proved to be cowlesite. The cowlesite was not found to occur in the same vug with other
zeolites. The assemblage from Table Mountain includes
laumontite, stilbite,
thomsonite, chabazite,
analcime, apophyllite,
mesolite, natrolite,
scolecite, lévyne (with an
overgrowth of offretite) and
garronite
(AM 60.951-956).
Cowlesite from North Table Mountain -
Image
At Neer Road, Goble, Columbia County, Oregon, USA, cowlesite occurs sparsely in small vugs in
basalt exposed by road cuts. The cowlesite forms thin, grey,
blue-grey to white cavity linings, growing as radially oriented blades. These linings are commonly 0.5 mm thick, but a
few sprays of blades up to 2 mm have been found. None of the blades are thicker than 2 microns. ln about 90% of the
vugs in which cowlesite has grown, it is the only zeolite. In the
remaining vugs it occurs in the following sequence: apophyllite (earliest),
analcime, cowlesite,
garronite, phillipsite,
lévyne and thomsonite
(AM 60.951-956).
Cowlesite from Neer Road - Image
At Beech Creek Quarry, Mount Vernon, Grant County, Oregon, USA, cowlesite occurs in cavities in
basalt. Although analcime,
lévyne (with its offretite
overgrowth), phillipsite,
thomsonite, heulandite,
stilbite, chabazite and
mesolite all occur at this locality, cowlesite has been found only
with lévyne. The cowlesite clearly preceded the
lévyne, which generally was one of the earliest
zeolites to form.
The cowlesite forms grey to blue-grey linings up to 0.3 mm thick and compact balls of radiating blades.
Terminations project above the lining surface, giving it a rough appearance
(AM 60.951-956).
Cowlesite from the Beech Creek Quarry -
Image
At Spray, Wheeler County, Oregon, USA, the basalts exposed in road cuts
10 miles northeast of Spray contain sparse cowlesite. Analcime,
lévyne (with offretite overgrowths),
phillipsite, thomsonite,
chabazite, mesolite and
apophyllite all occur in fair abundance at this locality. Cowlesite
appears in cavities with no other zeolites. lndividual sprays about 0.5 mm high
with delicate individual crystals have grown on globular clay cavity
linings. As in all localities the crystals are very thin blades with sharp terminations
(AM 60.951-956).
Cowlesite from Spray - Image
At an Unnamed Zeolite occurrence, Capitol Peak, Olympia, Thurston County, Washington, USA, one small specimen
containing cowlesite was found. The cowlesite occurs directly with no other
zeolites, but in nearby vugs lévyne,
chabazite, stilbite (variety
epidesmine) and mordenite have been found.
The cowlesite occurs in delicate white sprays of blades 0.25 mm long, as well as cavity linings with the same
thickness. The zeolite appears to have grown at least partially at the same
time as an iron smectite clay
(AM 60.951-956).
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