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Formula: KCa2(Be2AlSi12)O30.H2O
Cyclosilicate (ring silicate), osumilite group,
beryllium-bearing mineral
Crystal System: Hexagonal
Specific gravity: 2.46 to 2.61 measured, 2.524 calculated
Hardness: 6
Streak: White
Colour: Colourless, white, greenish white, yellowish white
Solubility: Generally insoluble in common acids, some is slightly soluble in hydrochloric acid; soluble in HF
(Dana)
Common impurities: Na
Environments:
Pegmatites
Hydrothermal environments
Milarite can form in solutions of pH ranging from 7 (neutral) to 9 (slightly alkaline). The best crystals come
from the more alkaline environments. In some cases milarite is a product of the alteration of
beryl in pegmatites.
In Alpine-type clefts milarite occurs chiefly in intrusive bodies of
syenite or in miarolytic cavities in
aplite
veins, commonly associated with orthoclase,
actinolite, titanite,
calcite, apatite,
zeolites and, in some cases, quartz.
Chlorite group minerals coat and partially replace milarite in many
specimens
(Minrec 35.5.405-418).
Milarite is a low-temperature hydrothermal mineral crystallising at 200 to 250oC and low
pressure (Dana). Other associated minerals include orthoclase,
albite, fluorite,
beryl, phenakite,
bertrandite, bavenite,
minasgeraisite-(Y), quartz,
calcite, muscovite and
chlorite
(HOM).
Localities
At the Haitzingalmstollen, Bad Gastein, St. Johann im Pongau District, Salzburg, Austria, milarite crystals to
4 mm are associated with
titanite
(Minrec 35.5.410).
At Wiesbachrinne, Bramberg am Wildkogel, Zell am See District, Salzburg, Austria, cabinet sized specimens of
chloritised milarite crystals on
orthoclase
have been found in an outcrop of gneiss, with individual crystals to
4.5 cm
(Minrec 35.5.410).
At Laperwitzgraben, Kals am Großglockner, Lienz District, Tyrol, Austria milarite crystals to 2 cm have been
found with pericline
(Minrec 35.5.410).
At the Jaguaraçu pegmatite, Jaguaraçu, Minas Gerais, Brazil, milarite crystals to 3 cm have been found in vugs
in albite
(Minrec 35.5.408).
At Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Quebec, Canada, milarite occurs on
pectolite crystals in marble
xenoliths
(Dana).
At the Chardonnet Peak, Mont Blanc massif, Haute-Savoie, France, milarite crystals to 3 mm occur on pink
fluorite crystals
(Minrec 35.5.408).
At Tittling, Passau District, Lower Bavaria, Bavaria, Germany, crystals of milarite to 5 mm, formed from the
alteration of beryl, have been found with rosettes of
bavenite crystals and bavenite
pseudomorphs after
beryl, associated with quartz,
albite and chlorite
AM 76.1836-1856, Minrec 35.5.408).
At Oberfrauenwald, Waldkirchen, Lower Bavaria, Bavaria, Germany, milarite crystals to 2 mm occur with
quartz, bavenite and
moraesite
(Minrec 35.5.408).
At the Himmelleiten quarry, Roßbach, Wald, Cham, Upper Palatinate, Bavaria, Germany, milarite crystals to
0.5 mm occur in
aggregates of fibrous bavenite crystals
(Minrec 35.5.408).
Near Henneberg, Weitisberga, Wurzbach, Saale-Orla District, Thuringia, Germany, microcrystals of milarite occur
with
beryl
(Minrec 35.5.408).
At Tanno, Chiavenna, Sondrio Province, Lombardy, Italy, a druse of microcrystals of milarite and
bavenite on
feldspar has been found
(Minrec 35.5.408).
At Monte Cervandone area, Devero Alp, Baceno, Verbano-Cusio-Ossola Province, Piedmont, Italy, milarite crystals
to 2 mm have been found on gneiss with
muscovite,
stilbite, quartz,
titanite and hematite
(Minrec 35.5.408).
At Val di Crana, Toceno, Verbano-Cusio-Ossola Province, Piedmont, Italy, a single specimen has been found with
milarite crystals to 1 mm on albite with
bavenite,
quartz, fluorite and
spessartine
(Minrec 35.5.408).
At Vento Valley, Prettau, Puster Valley District, South Tyrol, Trentino-Alto Adige, Italy, milarite crystals to
5.5 cm have
been found in a cleft in a band of aplite in
amphibolite gneiss,
associated with
calcite, orthoclase and smoky
quartz, or as floaters to 3.5 cm
(Minrec 35.5.408-410).
At Tanakamiyama, Otsu City, Shiga Prefecture, Kinki Region, Honshu Island, Japan, prisms of milarite to 1 mm
long are found in a pegmatite associated with
microcline, schorl,
and quartz
(R&M.6.525).
At the Kent Massif, Karkaraly, Karaganda Region, Kazakhstan, crystals of smoky
quartz
have been found with inclusions of milarite to 2 cm
(Minrec 35.5.408).
At the Valenciana mine, Guanajuato, Guanajuato Municipality, Guanajuato, Mexico, crystals of milarite to 18 mm
occur as aggregates of prisms associated with adularia and minor
quartz
AM 76.1836-1856), and as crystals to 3 cm intimately intergrown with
orthoclase with
tiny quartz crystals grown on the prism faces of the milarite
(Minrec 35.5.407).
At Klein Spitzkopje granite stock, Spitzkopje Area, Karibib, Erongo Region, Namibia, in
uranium-enriched
syenite, milarite crystals to 2.5 cm occur embedded in
calcite and associated with quartz and
albite
(Minrec 35.5.407-408).
Near Fuglevika, Stavern, Larvik, Vestfold, Norway, milarite crystals to 3 mm occur in
syenite
pegmatites with
microcline,
albite and aegirine
(Minrec 35.5.408).
At the Himberg quarry, Ramnes, Re, Vestfold, Norway, milarite crystals to 7mm occure in miarolytic cavities in
syenite
(Minrec 35.5.408).
At the Ermakovskoe Be Deposit, Kizhinginsky District, Buriatia Republic, Zabaykalsky Krai, Russia, milarite
crystals to 4 cm
occur with bavenite
(Minrec 35.5.408).
At Vorderer Zinggenstock, Zinggenstöcke, Oberaar lake area, Grimsel area, Hasli Valley, Bern, Switzerland, fine
milarite crystals to 2 cm with orthoclase and smoky
quartz
(Minrec 35.5.412).
At the Cristallina Valley, Val Medel, Medel, Surselva Region, Grisons, Switzerland, milarite occurs with
orthoclase, smoky quartz and
apatite
(Minrec 35.5.411).
The type locality, the Giuv Valley, Tujetsch, Surselva Region, Grisons, Switzerland, has yielded some of the finest
specimens
of milarite in the world; it occurs on a syenite matrix together
with
orthoclase, apatite, smoky
quartz and a little actinolite
(Minrec 35.5.415).
At Göscheneralp, Göschenen Valley, Göschenen, Reuss Valley, Uri, Switzerland; milarite occurs sparingly with
quartz, fluorite and
calcite
(Minrec 35.5.411).
At the Gischi glacier, Binn, Goms, Valais, Switzerland, milarite crystals to 4 mm occur with pink
fluorite
(Minrec 35.5.411).
At Fieschertal, Goms, Valais, Switzerland, milarite is associated with
orthoclase,
epidote, hematite and aggregates of
fibrous bavenite. The largest known crystal of milarite, 9.2 cm
long, was collected here
(Minrec 35.5.413).
In New Hampshire, USA, milarite is found in the miaroles of
niobium-yttrium-fluorine
(NYF) pegmatites. It forms in an alkaline environment with a
pH of approximately 8 to 9. Crystals can reach 2 cm in length and 2 mm in width, but most are only a few millimeters or
less long. Crystals often occur in parallel groups of thin prisms. In New Hampshire, milarite is found only at
the Moat Mountain, Government pit, and nearby Frechette gravel pit localities. There is considerable
fluorite present in these
pegmatites that could dissolve with late-stage fluids and
provide the calcium needed to form milarite
(R&M 97.3.227-228).
At the Middle Moat Mountain locality, Hale's Location, Carroll County, New Hampshire, USA, white hexagonal crystals of
milarite with basal terminations were found in clay and rubble that
came from a mineralised seam in decomposed granite; the seam contained
small miaroles with smoky quartz,
microcline and mica.
Milarite is a relatively rare mineral usually found in crystals of only a few millimeters or less, but the best
Moat Mountain crystal is a sharp, lustrous, colourless to white hexagonal prism that is 2.1 × 0.7 cm in size; it is the
finest known milarite crystal ever found in North America
(R&M 97.3.227-228).
At the Foote Lithium Company mine, Kings Mountain Mining District, Cleveland county, North Carolina, USA,
milarite crystals
to 3mm are associated with albite
(Minrec 35.5.407).
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