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Formula: Na4Al3Si9O24Cl
Tectosilicate (framework silicate), scapolite group, forms a series with
meionite
Crystal System: Tetragonal
Specific gravity: 2.5 to 2.62 measured, 2.54 calculated
Hardness: 5½ to 6
Streak: White
Colour: Colourless, white, bluish, brownish, yellowish, violet, greenish
Solubility:
Common impurities: Fe,Ca,K,S
Environments
Volcanic igneous environments
Pegmatites
Metamorphic environments
Hydrothermal environments
Marialite typically occurs in regionally metamorphosed rocks, especially
marble, calcareous gneiss,
granulite and greenschist. It also
occurs in skarn, some pegmatites,
pneumatolytically or hydrothermally altered mafic igneous rocks and ejected volcanic blocks.
Associated minerals include plagioclase, garnet,
pyroxenes, amphiboles,
apatite, titanite and
zircon
(HOM, Mindat).
Localities
The Aricanga hill, Aracruz, Espírito Santo, Brazil, was, in the latter part of the 20th century, the main
producer of scapolite in all of Brazil. It occurred in a
granitic
pegmatite that is now inside the Aricanga County
Natural Park and completely overgrown with vegetation. Minerals found in the now-closed mine included
microcline, quartz,
biotite, beryl,
rutile, uranium minerals,
magnetite and the
scapolite series mineral marialite.
The marialite crystals are colourless to pale yellow to deep yellow, and up to 15 cm long and 6 cm
wide. Many museum-quality specimens have been found
(Minrec 54.735-737).
The Purple Diopside Mound, Rose Road, Pitcairn, St. Lawrence county, New York, USA, is situated in
marble. The development of veins of large crystals probably occurred as
a result of fluid penetration from a concurrent intrusion. Many of the minerals of interest to collectors formed during
this primary event, with additional species resulting from the
subsequent alteration of scapolite. There seems to be little, if any,
secondary, late-stage mineralisation present.
Marialite occurs as white outer zones on grey meionite crystals
(R&M 90.5.446, R&M 96.6.550). It has strong yellow-orange to orange fluorescence under long wave UV
(R&M 97.5.443).
Marialite pseudomorphs are extremely common in the branched
scapolite vein
running up the middle of the mound. Some dark grey,
glassy meionite crystals are altered from the surface inward to a cream-white to pale tan layer of
marialite. The following observations indicate that these
pseudomorphs resulted from later alteration of preexisting
meionite crystals:
No marialite crystals have been found without a meionite core.
The marialite/meionite boundary shows an irregular contact typical
of alteration rather than a sharp boundary resulting from overgrowth.
The ultrastructure of the internal meionite reveals a smooth texture typical
of a single crystal domain, whereas that of the external marialite layer shows a jumble of small crystallised
regions of varying orientation typical of an alteration structure.
Minute acicular crystals of pyrite extend continuously for long distances in
the meionite interior and are crystallographically oriented; these thin
pyrite filaments extend across the boundary into the marialite
exterior zone with continuity and the same orientation, but they are discordant with the myriad regions of
marialite of different orientation.
Taken together, these data suggest that the pseudomorphs are the result
of the alteration of meionite, to marialite, proceeding from the
crystal surface inward. The altering fluids must have been enriched in sodium and chlorine and capable of dissolving
and removing calcium and carbonate
(R&M 97.5.434-444).
At the Selleck Road Tremolite and Tourmaline Locality,
West Pierrepont, St. Lawrence County, New York, USA, marialite occurs as prismatic crystals to 10 cm in complex clusters to 20 cm.
Most crystals are altered to creamy white microcline, at least on their surfaces, and many have
been completely replaced by that mineral. Unaltered marialite is most common in the Walter-Crump pit, the Walter-Wallace pit, and the
Carlin trench.
At the Walter-Crump pit, tremolite crystals, large diopside
crystals, some altered to, and overgrown by, tremolite, and
quartz crystals formed along the contacts a series of convoluted contacts between
marble and
tremolite-diopside rock. Locally masses of
lavender marialite were encountered in groups of interlocking crystals, mostly altered to
microcline except in the centres.
At the Walter-Wallace pit significant specimens of lavender marialite crystals, often partially replaced by creamy white
microcline, were recovered from a large pocket of
fluor-uvite crystals.
At the Carlin trench marialite was found in a vein that also contained phlogopite triplet
twins, albite, microcline,
heulandite-Ca, and fluor-uvite
(R&M 91-2.123).
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