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Formula: Be3Mn2+4(SiO4)3S
Tectosilicate (framework silicate), helvine group, beryllium and
manganese bearing mineral, forms series with
genthelvite and with danalite
Crystal System: Isometric
Specific gravity: 3.2 to 3.44 measured, 3.23 calculated
Hardness: 6 to 6½
Streak: White
Colour: Golden yellow, brown, red, grey-yellow, yellow-green
Luminescence: Red cathodoluminescence
Solubility: Dissolves slowly in boiling hydrochloric acid (1:1), forming a silica gel and hydrogen sulphide
Common impurities: Al,Fe,Zn,Ca
Environments
Plutonic igneous environments
Pegmatites
Metamorphic environments
Helvine may be locally abundant in granites,
granite
pegmatites,
gneisses, contact
zones and skarns. Associated minerals include
garnet, magnetite,
fluorite, chlorite,
diopside and vesuvianite
(HOM).
Localities
At Tongbei, Yunxiao County, Zhangzhou, Fujian, China, orange-brown helvine occurs with pale green and pale mauve
fluorite and orange spessartine
(AESS).
Helvine from Tongbei - Image
At Loudervielle, Bagnères-de-Bigorre, Hautes-Pyrénées, Occitanie, France, helvine has been found in a zone of
manganiferous mineralisation associated with layers of
jasper. Associated minerals include
rhodochrosite, rhodonite,
quartz, tephroite,
spessartine, friedelite,
braunite, stilpnomelane,
chlorite, alleghanyite,
sonolite, hübnerite,
alabandite, sphalerite and
welinite. The crystals of helvine are greenish lemon-yellow, up to
1 cm in length, and exhibit red cathodoluminescence.
There is a complete solid solution between helvine and danalite, and
between danalite and
genthelvite. Intermediate compositions between
genthelvite and helvine are lacking
(CM 32.1.111-120).
There are two co-type localities, the Brüder Lorenz mine and the St. Richard Mine, both at Breitenbrunn, Breitenbrunn,
Erzgebirgskreis, Saxony, Germany.
Helvine from the Brüder Lorenz Mine - Image
Helvine from the St. Richard Mine - Image
At Lexington mine, Walkerville, Butte Mining District, Silver Bow County, Montana, USA, a specimen of helvine
was found, which weighs about four pounds, and is largely rhodonite and
rhodochrosite, through which sporadic grains of sulphide minerals
are scattered. The sulphides include pyrite,
galena and sphalerite, but no
alabandite was found. Helvine occurs as sparse lemon-yellow grains
up to 2 mm across, and as veinlets about 1 mm wide in the midst of the pink
manganese minerals.
In the examined sections, helvine occurs only in or near the
rhodonite veinlets with which sulphides are associated, and it was,
therefore, one of the last minerals to be deposited
(AM 22.6.803–804).
In New Hampshire, USA, helvine group minerals usually occur in NYF
(niobium Nb, yttrium Y and fluorine F)
pegmatites, although occurrences at the Iron Mountain mine in
Bartlett and the Madisin lead mine in Madison are exceptions
(R&M 97.3.221-224).
Helvine from New Hampshire - Image
At Grandview Mine, Otero county, New Mexico, USA, helvine has been found in a
zinc replacement deposit in
limestone. The ore minerals are
sphalerite and galena with local
rare concentrations of chalcopyrite. Associated minerals include
garnet, epidote,
serpentine, magnetite,
fluorite, pyrite,
quartz, calcite and
chlorite, with traces of scheelite.
The limestone has been recrystallised and locally contains
considerable garnet.
In a specimen of fluorite from a vug in the ore body tiny tetrahedrons of
yellow helvine were discovered, in part incrusting the surface of the
fluorite and in part embedded in it.
Sphalerite was also present. The crystals of helvine are up to a
millimeter across and smaller ones form clusters of interlocking crystals up to 3 millimeters across, scattered
sparsely on the fluorite
(AM 33.648-649).
Helvine from the Grand View Mine - Image
At Discovery Gulch, Iron Mountain No. 2 District, Sierra County, New Mexico, USA, most of the known coarsely crystalline
helvine occurs in small bodies of tactite along a contact between
recrystallised limestone and a plug of coarsely
porphyritic rhyolite.
Smaller amounts have been found in tactite lenses that lie in
recrystallised limestone at and near contacts with masses of
aplite and fine-grained
granite. The iron-rich host rock
for the helvine is composed of magnetite and
fluorite, with minor amounts of
biotite, chlorite and
diopside. Garnet is rare to absent.
The tactite is characteristically layered. Some of the bands consist of
solid helvine, but most helvine-bearing layers are aggregates of
fluorite and helvine; the intervening layers are solid
magnetite or
biotite-chlorite aggregates 3 to 10
mm thick. Irregular pods of coarsely crystallized helvine, with maximum dimensions of 1 inch by 3 inches by 4
inches, are present but are not common.
The helvine is amber-brown to mahogany-red with a vitreous to resinous luster. Much of it is stained dark brown
or nearly black by iron and manganese oxides. Most of the helvine is
massive, but well-formed crystals occur in vugs, commonly associated with
quartz and fluorite. Although most of
the crystals are less than 4 mm across, some reach 12 mm on an edge
(AM 29.169-171).
At the North End area, Iron Mountain No. 2 District, Socorro county, New Mexico, USA, A small quantity of
helvine was found that has an index of refraction lower than that of the more typical and more abundant
helvine from Discovery Gulch; this indicates a higher manganese and
lower iron-plus-zinc content. These lower
index grains were found in crushed material and their association is not known
(AM 29.169).
Helvie from the Iron Mountain No. 2 District -
Image
At the Miller Mine, Granite Mining District, Beaver County, Utah, USA, the country rock consists of
marble and tactite, both
of which are intruded by granite dikes. The freshest dike rock consists
of quartz, orthoclase and
oligoclase, together with minor mica
and chlorite. Accessory minerals include
magnetite, fluorite and
allanite(?).
Helvine and beryl occur in close proximity both in altered dike rock and
in sugary-textured marble. Neither has been identified by the writer in
tactite. The largest helvine fragments were obtained from
brecciated marble on the
footwall of the dike, and beryl was found in close association. Helvine
was obtained also from altered dike rock on the lowest level of the northeriy shaft. The helvine is in parts of
the dike that contain abnormal amounts of mica, a black uranium mineral, and such
sulphide minerals as sphalerite,
galena and
chalcopyrite. Fluorite is
common and at places constitutes several per
cent of the rock. Topaz was identified in several thin sections, and
magnetite locally is relatively abundant. Carbonate minerals are abundant
throughout the altered dike. Secondary uranium minerals coat the
fractures in the dike at several places.
The helvine occurs as anhedral to subhedral masses as much as 1 inch long in both dike rock and in fractured
marble. Vugs in the fractured
marble contain minute grains of helvine. The helvine in
altered dike rock exhibits a distinct preference for dark-green mica in
replacement. In one specimen of altered dike rock, helvine replaces carbonate formed from altered
feldspar, and hence it appears that the helvine is later than the
general alteration of the dike. The helvine is tawny-colored with a vitreous lustre. It contains small grains of
a black, opaque mineral, possibly magnetite, and locally small grains of
glassy topaz
(AM 47.395-398).
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