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Formula: Be3Fe2+4(SiO4)3S
Tectosilicate (framework silicate), helvine group, forms a series with
genthelvite and with helvine,
beryllium-bearing mineral
Specific gravity: 3.28 to 3.46
Hardness: 3½ to 6
Streak: Grey-white
Colour: Pink, grey, yellow, reddish brown, red
Solubility: Gelatinises with acids
Common impurities: Mn,Zn,Ca,S
Environments
Plutonic igneous environments
Pegmatites
Metamorphic environments
Hydrothermal environments
Danalite occurs in granite, granite
pegmatites, contact metamorphic and hydrothermal environments,
skarn and gneiss. In
skarn it is associated with magnetite,
garnet and fluorite; in
tin-bearing pegmatites it is associated with
albite,
cassiterite, pyrite and
muscovite; in hydrothermal deposits it is associated with
arsenopyrite, quartz and
chlorite
(HOM).
Localities
At Needlepoint Mtn, McDame area, Liard Mining Division, British Columbia, Canada, danalite occurs in
skarn in limestone,
associated with
magnetite, quartz,
chlorite, fluorite and native
bismuth
(AM 65.358).
At the Mihara mine, Mihara City, Hiroshima, Japan, danalite occurs with
phenakite in
monzonite near a skarn
contact
(AM 65.358).
At an unspecified locality in Russia, danalite has been reported in pegmatites replacing
beryl; it is
in turn replaced by bertrandite,
phenakite,
pyrite and hematite
(AM 65.358).
At the Precambrian Russian platform, danalite altered by hematite occurs
in quartz veins in altered granite
and dolerite. Helvine,
phenakite, muscovite,
calcite, magnetite and
aegirine occur in related rocks
(AM 65.358).
In the Russian Far East, in complex tin-rare metal deposits, danalite occurs in
plagioclase-clinopyroxene
skarn in marble, associated
with cassiterite, scheelite,
garnet, fluorite and
arsenopyrite.
Also, danalite occurs in
diopside-magnetite
skarn with chrysoberyl,
phlogopite, vesuvianite,
epidote, garnet,
hastingsite, fluorite,
cassiterite and chalcopyrite
(AM 65.358).
At Lindsay's Leap, Newcastle, Mourne Mountains, County Down, Ulster, Northern Ireland, UK, danalite occurs rarely as small crystals and
grains on joint planes and in small cavities with quartz, saponite
and stilbite-Ca. It is later in the paragenesis than quartz and
feldspars, but earlier than the low-temperature zeolites
(MM 25.25, 27).
At the Cheyenne Mining District, El Paso county, Colorado, USA, small
genthelvite crystals which
sometimes occur as epitaxial overgrowths on danalite have been found in a pegmatite pocket. The
genthelvite/danalite crystals were present in a small cavity that was
lined with
microcline crystals, some with epitaxial
albite
overgrowths, and sometimes covered with prisms of prosopite to 5 mm. Accessory
minerals include
ilmenite, columbite-(Fe) and
bastnäsite-(Ce). Late-stage
genthelvite coatings are
present on exposed danalite faces. The mineral assemblage is, in part, the result of the alkaline nature of the
melt that leads to the
formation of helvine-group minerals rather than
beryl. Decreasing
sulphur activity from early to late pocket-forming stages resulted in the change
from crystallisation of
danalite to genthelvite. Increasing oxygen activity resulted in both
the cessation of
danalite crystallisation and a change in crystallising oxide phases, from
siderite to
hematite to limonite
(R&M 93.3.259-260).
At Mount Rosa, El Paso County, Colorado, USA, beryl is absent, but late-stage to
secondary
beryllium-bearing minerals are present. A few
genthelvite crystals have been found as epitactic overgrowths on
danalite, and genthelvite coatings are also present on some of the
exposed danalite faces.
Danalite is rare in the Mount Rosa Complex, and the presence of
genthelvite/danalite overgrowths
record subtle changes in the late-stage fluids responsible for their crystallisation.
Danalite crystallises in reducing conditions, whereas
genthelvite is restricted to relatively oxidising conditions
(R&M 95.3.271-272).
The type locality is Rockport, Essex county, Massachusetts, USA.
At the Cape Ann Granite Company quarry, Gloucester, Essex county, Massachusetts, USA, danalite occurs in cavities
in granite and is altered to
siderite,
phenakite, quartz,
pyrite and sphalerite
(AM 65.358).
At the Iron Mountain mines, Bartlett, Carroll county, New Hampshire, USA, danalite occurs in metasomatically
replaced granite,
danalite-helvine solid solutions are
found overgrowing phenakite, with
magnetite,
pyrite, sphalerite,
quartz, galena,
fluorite, hematite and
pyroxene
(AM 65.358).
At Iron Mountain, Sierra county, New Mexico, USA, helvine and danalite
occur in a metamorphic contact zone between limestone and
rhyolite
and granite. The host rock is a dark, banded
tactite
composed chiefly of magnetite,
fluorite,
chlorite and diopside. Danalite
is associated with
fluorite, magnetite,
grossular, chlorite,
biotite, vesuvianite,
epidote, tilleyite and chamosite
variety
thuringite.
(AM 29.163-191, AM 65.358).
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