Cyclosilicate
Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust.
In mineralogy, silica (silicon dioxide, ) is usually consid ...
, image = Baotite-661893.jpg
, imagesize = 260px
, alt =
, caption = Baotite from Sheep Creek, Mineral Point District, Ravalli County, Montana
, formula = Ba4Ti4(Ti,Nb,Fe)4(Si4O12)O16Cl
, IMAsymbol=Bao
, molweight =
, strunz = 9.CE.15
, system =
Tetragonal
In crystallography, the tetragonal crystal system is one of the 7 crystal systems. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a squar ...
, class = Dipyramidal (4/m) H-M symbol: (4/m)
, symmetry = ''I''41/a
, color = light brown to black
, habit = anhedral to subhedral, prismatic and striated parallel to (001)
, twinning =
, cleavage = fair on {110}
, fracture = hackly
, tenacity = brittle
, mohs = 6
, luster = vitreous
, refractive = nω = 1.94, nε > 2.00
, opticalprop = Uniaxial (+)
, birefringence =
, dispersion =
, pleochroism = strong
, fluorescence=
, absorption = E > O
, streak =
, gravity =
, density = 4.42-4.71 g/mL (measured), 4.69 g/mL (calculated)
, fusibility =
, diagnostic =
, solubility =
, diaphaneity =
, other =
, references = Anthony, J.W., Bideaux, R., Bladh, K., and Nichols, M. (2003) Baotite Ba4(Ti,Nb)8Si4O28Cl. Handbook of Mineralogy, Mineral Data Publishing (Republished by the Mineralogical Society of America) Fact sheet /ref>
Baotite Ba4Ti4( Ti, Nb, Fe)4( Si4O12)O16Cl is a rare mineral recognized as having a unique four-fold silicate ring.Chakhmouradian, A.R. and Mitchell, R.H. (2002) The mineralogy of Ba- and Zr-rich alkaline pegmatites from Gordon Butte, Crazy Mountains (Montana, USA): comparisons between potassic and sodic agpaitic pegmatites. Contributions to Mineralogy and Petrography, 143, 93-114. Crystals are
tetragonal
In crystallography, the tetragonal crystal system is one of the 7 crystal systems. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a squar ...
, though commonly deformed to the extent of appearing
monoclinic
In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic s ...
. Named for the locality of first discovery, Baotou, China, baotite has been found in
hydrothermal vein
In geology, a vein is a distinct sheetlike body of crystallized minerals within a rock. Veins form when mineral constituents carried by an aqueous solution within the rock mass are deposited through precipitation. The hydraulic flow involved ...
s and alkalic rocks in various locations around the world.
Structure
Simonov first determined the crystal structure of baotite in which (Ti, Nb, Fe)-
octahedra
In geometry, an octahedron (plural: octahedra, octahedrons) is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet a ...
share edges, forming chains and cross-linking at the corners forming a 4-fold
screw axis
A screw axis (helical axis or twist axis) is a line that is simultaneously the axis of rotation and the line along which translation of a body occurs. Chasles' theorem shows that each Euclidean displacement in three-dimensional space has a scre ...
in the (001); these columns are analogous to those in
rutile
Rutile is an oxide mineral composed of titanium dioxide (TiO2), the most common natural form of TiO2. Rarer polymorphs of TiO2 are known, including anatase, akaogiite, and brookite.
Rutile has one of the highest refractive indices at visib ...
.Simonov, V.I. (1960) Baotite, a mineral with a metasillicate ring (Si4O12). Kristallografiya, 5, 544-546 (in Russian). Abs. in American Mineralogist, 46, 466, 1961. Four silicate tetrahedra share corners creating characteristic rings in the plane perpendicular to the c axis.Shinno, I. and Li, Z. (1998) Mössbauer studies of baotite and bafertisite. Hyperfine Interactions, 116, 189-196. The barium cation is between the rings and rutile columns, while chloride fills the void between each pair of rings.Cooper, A.F. (1996) Nb-rich baotite in carbonatites and fenites at Haast River, New Zealand. Mineralogical Magazine, 60, 473-482. Chlorine's presence is not necessary for the structure to balance
electrostatically
Electrostatics is a branch of physics that studies electric charges at rest (static electricity).
Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for amber ...
.
Geologic occurrence
The first sample of baotite was found with galena,
pyrite
The mineral pyrite (), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula Fe S2 (iron (II) disulfide). Pyrite is the most abundant sulfide mineral.
Pyrite's metallic luster and pale brass-yellow hue giv ...
,
albite
Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. It represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula . It is a tectosilicate ...
,
aegirine
Aegirine is a member of the clino pyroxene group of inosilicate minerals. Aegirine is the sodium endmember of the aegirine-augite series. Aegirine has the chemical formula Na Fe Si2 O6 in which the iron is present as Fe3+. In the aegirine-augit ...
quartz
Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
vein cutting
quartzite
Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tec ...
Peng, C.J. (1959) The discovery of several new minerals of rare elements. Ti-Chin Ko-hsuch, 10 (in Chinese). Abs. in American Mineralogist, 45, 754, 1960. at the
Bayan Obo
Bayan'obo Mining District, ( Mongolian: ''Bayan Oboɣ-a Aɣurqai-yin toɣoriɣ'', Баян-Овоо Уурхайн тойрог ( mn, italic=yes, "rich" + ovoo); ), or Baiyun-Obo or Baiyun'ebo, is a mining town in the west of Inner Mongolia, ...
Mine in China. Grains from
Ravalli County, Montana
Ravalli County is a county in the southwestern part of the U.S. state of Montana. As of the 2020 census, the population was 44,174. Its county seat is Hamilton.
Ravalli County is part of a north–south mountain valley bordered by the Sapphir ...
were found in a thin calcite crust on masses of eschynite within a carbonatic vein.Heinrich, E.W., Boyer, W.H. and Crowley, F.A. (1962) Baotite (Pou-t’ou-k’uang) from Ravalli County, Montana. American Mineralogist, 47, 987-993. Baotite also occurs at
Haast River
The Haast River / Awarua is a river on the West Coast of the South Island of New Zealand. The Māori name for the river is Awarua. It drains the western watershed of the Haast Pass. The Haast River is in length, and enters the Tasman Sea n ...
, New Zealand as an accessory phase of
carbonatite
Carbonatite () is a type of intrusive or extrusive igneous rock defined by mineralogic composition consisting of greater than 50% carbonate minerals. Carbonatites may be confused with marble and may require geochemical verification.
Carbonati ...
,
fenite
Fenite is a metasomatic alteration associated particularly with carbonatite intrusions and created, very rarely, by advanced carbon dioxide alteration (carbonation) of felsic and mafic rocks. It is characterised by the presence of alkali feldspar, ...
and hydrothermal fluid veins associated with a
dike swarm
A dike swarm (American spelling) or dyke swarm (British spelling) is a large geological structure consisting of a major group of parallel, linear, or radially oriented magmatic dikes intruded within continental crust or central volcanoes ...
. The
dike
Dyke (UK) or dike (US) may refer to:
General uses
* Dyke (slang), a slang word meaning "lesbian"
* Dike (geology), a subvertical sheet-like intrusion of magma or sediment
* Dike (mythology), ''Dikē'', the Greek goddess of moral justice
* Dikes ...
intrusion of mantle-derived magmas can likely be attributed to the close proximity of the
Alpine fault
The Alpine Fault is a geological fault that runs almost the entire length of New Zealand's South Island (c. 480 km) and forms the boundary between the Pacific Plate and the Indo-Australian Plate. The Southern Alps have been uplifted on the f ...