Pabstite is a

barium Barium is a chemical element; it has symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element. Th ...

tin Tin is a chemical element; it has symbol Sn () and atomic number 50. A silvery-colored metal, tin is soft enough to be cut with little force, and a bar of tin can be bent by hand with little effort. When bent, a bar of tin makes a sound, the ...

titanium Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in ...

silicate mineral 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, the crystalline forms of silica (silicon dio ...

that is found in contact metamorphosed

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

. It belongs to the benitoite group of minerals. The chemical formula of pabstite is . It is found in

Santa Cruz, California Santa Cruz (Spanish language, Spanish for "Holy Cross") is the largest city and the county seat of Santa Cruz County, California, Santa Cruz County, in Northern California. As of the 2020 United States census, 2020 census, the city population ...

. The

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macros ...

system of the mineral is hexagonal.

Composition

Pabstite is 37.7% SiO₂, 3.8% TiO₂, 24.4% SnO₂ and 33.2% BaO. However, Ti and Sn could vary from point to point by approximately ±0.5% TiO₂ and ±1% SnO₂. Pabstite is a tin bearing analog of benitoite. Although, (Sn⁴⁺ = 0.71 Å) and (Ti⁴⁺= 0.68Å) have similar charge and ionic size, it is uncommon to find them substituting each other.

Geologic occurrence

Pabstite commonly occurs as anhedral crystals and masses that vary in their color from colorless to white.Dunning, G. E & Cooper, J. F. Jr. (1986). "Mineralogy of the Kalkar Quarry, Santa Cruz, California." '' Mineralogical Record, 17'', 315- 326. They produce a pink tinge when they are freshly broken. Large amounts of pabstite were found in Santa Cruz as fracture filling and disseminated grains in recrystallized siliceous limestones.Wainwright, John E. N & Evans, Bernard W. (1965). "Pabstite,¹ the tin analogue of benitoite." ''The American Mineralogist, 50'', 1164–1169. This is geologic evidence of contact

metamorphism Metamorphism is the transformation of existing Rock (geology), rock (the protolith) to rock with a different mineral composition or Texture (geology), texture. Metamorphism takes place at temperatures in excess of , and often also at elevated ...

. In addition, pabstite can be found in Rush Creek in California when benitoite contains small amounts of tin. It is commonly occurs in rocks that contain

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

tremolite Tremolite is a member of the amphibole group of silicate minerals with composition Ca2(Mg5.0-4.5Fe2+0.0-0.5)Si8O22(OH)2. Tremolite forms by metamorphism of sediments rich in dolomite and quartz, and occurs in two distinct forms, crystals and fib ...

witherite Witherite is a barium carbonate mineral, Ba C O3, in the aragonite group. Witherite crystallizes in the orthorhombic system and virtually always is twinned. The mineral is colorless, milky-white, grey, pale-yellow, green, to pale-brown. The spec ...

phlogopite Phlogopite is a yellow, greenish, or reddish-brown member of the mica family of phyllosilicates. It is also known as magnesium mica. Phlogopite is the magnesium endmember of the biotite solid solution series, with the chemical formula KMg3AlSi3 ...

diopside Diopside is a monoclinic pyroxene mineral with composition . It forms complete solid solution series with hedenbergite () and augite, and partial solid solutions with orthopyroxene and pigeonite. It forms variably colored, but typically dull ...

, minor amounts of

forsterite Forsterite (Mg2SiO4; commonly abbreviated as Fo; also known as white olivine) is the magnesium-rich Endmember, end-member of the olivine solid solution series. It is Isomorphism (crystallography), isomorphous with the iron-rich end-member, fayalit ...

and taramellite. Pabstite can also be found associated with

galena Galena, also called lead glance, is the natural mineral form of lead(II) sulfide (PbS). It is the most important ore of lead and an important source of silver. Galena is one of the most abundant and widely distributed sulfide minerals. It crysta ...

cassiterite Cassiterite is a tin oxide mineral, SnO2. It is generally opaque, but it is translucent in thin crystals. Its luster and multiple crystal faces produce a desirable gem. Cassiterite was the chief tin ore throughout ancient history and remains ...

and

sphalerite Sphalerite is a sulfide mineral with the chemical formula . It is the most important ore of zinc. Sphalerite is found in a variety of deposit types, but it is primarily in Sedimentary exhalative deposits, sedimentary exhalative, Carbonate-hoste ...

Structure

Pabstite is considered the tin analog of benitoite. It has a hexagonal crystal system with a P6*2C space group. Its dimensions are as follows, a= 6.7037(7), c= 9.824(1) Å3, C= 382.3(1) Å3, Z=2. Pabstite has the structure of the benitoite group of minerals.Hawthorne, Frank C. (1987). The crystal chemistry of the benitoite group minerals and structural relations in (Si₃O₉) ring structures. ''Neues Jahrbuch fuer Mineralogie. Monatshefte. 1987'', 16–30. In the structure of pabstite, there are four oxygens surrounding the cations in a pseudo-tetrahedral arrangement. A three-membered

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, the crystalline forms of silica (silicon dio ...

ring (Si₃O₉) is formed by repeating the tetrahedron using space group symmetry. Quadrivalent

cations An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...

connect the rings to form a three-dimensional framework. Since the silicate rings have a geometry that is identical in all directions, a solid rigid unit is formed in the structure. In a distorted hexagonal antiprism arrangement, Ba, which has a high symmetry, is bounded by 12 oxygens. Two different BaـــO distances are present. ⁴⁺ Si³O⁹frameworks are connected by Ba cations which lead to a poor

cleavage Cleavage may refer to: Science * Cleavage (crystal), the way in which a crystal or mineral tends to split * Cleavage (embryo), the division of cells in an early embryo * Cleavage (geology), foliation of rock perpendicular to stress, a result of ...

Physical properties

Finding pabstite in the field is hard and rare. When using a shortwave

ultraviolet light Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of th ...

, bluish white fluorescence is revealed from the specimens. This property is commonly used to identify pabstite. Pabstite is colorless to white. The diameter of pabstite grains is usually less than 2 mm and they contain minute

fluid In physics, a fluid is a liquid, gas, or other material that may continuously motion, move and Deformation (physics), deform (''flow'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are M ...

and solid inclusions. Its hardness is 6 on

Mohs scale of mineral hardness The Mohs scale ( ) of mineral hardness is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by the Ger ...

. Its density is 4.03 g/cm³ and it is uniaxial. The interference colors of pabstite are anomalous blue-violet and golden yellow. The

refractive indices In optics, the refractive index (or refraction index) of an optical medium is the ratio of the apparent speed of light in the air or vacuum to the speed in the medium. The refractive index determines how much the path of light is bent, or refrac ...

of pabstite are ω = 1.685±0.002 and ε = 1.674±0.002 which result in low

birefringence Birefringence, also called double refraction, is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are described as birefrin ...

and absent

dichroism In optics, a dichroic material is either one which causes visible light to be split up into distinct beams of different wavelengths (colours) (not to be confused with Dispersion (optics), dispersion), or one in which light rays having different P ...

Discovery and locations

Pabstite was first described in 1965 for an occurrence in the Kalkar quarry of Santa Cruz County, California. The mineral was named for

Adolf Pabst Adolf Pabst (30 November 1899, Chicago – 3 April 1990, Berkeley, California) was an American mineralogist and geologist. Biography Pabst received in 1925 his bachelor's degree at the University of Illinois and in 1928 his Ph.D. in geology an ...

(1899–1990) a mineralogy professor at the

University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California), is a Public university, public Land-grant university, land-grant research university in Berkeley, California, United States. Founded in 1868 and named after t ...

. Pabstite has also been reported from Tres Pozos,

Baja California Norte Baja California, officially the Free and Sovereign State of Baja California, is a state in Mexico. It is the northwesternmost of the 32 federal entities of Mexico. Before becoming a state in 1952, the area was known as the North Territory of B ...

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

and the Alai Range of the

Tien Shan Mountains The Tian Shan, also known as the Tengri Tagh or Tengir-Too, meaning the "Mountains of God/Heaven", is a large system of mountain ranges in Central Asia. The highest peak is Jengish Chokusu at high and located in Kyrgyzstan. Its lowest point is ...

Tajikistan Tajikistan, officially the Republic of Tajikistan, is a landlocked country in Central Asia. Dushanbe is the capital city, capital and most populous city. Tajikistan borders Afghanistan to the Afghanistan–Tajikistan border, south, Uzbekistan to ...

References

{{reflist Geology of California Cyclosilicates Barium minerals Tin minerals Titanium minerals Hexagonal minerals Minerals in space group 188