Celsian
Encyclopedia
Celsian is an uncommon feldspar
mineral
, barium aluminosilicate, Ba
Al
2Si
2O
8. The mineral occurs in contact metamorphic rock
s with significant barium
content. Its crystal system
is monoclinic, and it is white, yellow, or transparent in appearance. In pure form, it is transparent. Synthetic barium aluminosilicate is used as a ceramic
in dental fillings
and other applications.
The mineral is named after Anders Celsius
.
series and the celsian-orthoclase
series. It has some resemblance to anorthite
, and it has four distinct polymorphs
.
The essential elements are Si,Al,O and Ba. Some common impurities in the mineral are Fe, Ti, Mg, K and Ca. Celsian is stable from room temperature up to 1590 °C ( Lin and Foster,1968). The most common trace elements are potassium and calcium, in an analysis of the approximate chemical composition of celsian the following wt% were found:
• SiO2—35.1
• Al2O3---26.8
• BaO----35.8
• K2O-----2.3
Total:100.0 (Newham and Megaw,1960).
Celsian can be found in places like Wales, Zamora (Spain), Alaska, California, Sweden and Japan, also with hendricksite on the Franklin mines in New Jersey.
X-ray analysis shows that the values for the lattice parameters a, b, c axes and angles are approximately a=863 pm, b=131.0 pm, c=1400 pm and β=116°, θ=90° (Gay, 1956).
There are 8 formula units per cell, and the general position is eightfold, so all atoms can lie in general positions (Newnham and Megaw,1960). This structure is very similar to that of orthoclase and sanidine but differs in a couple of ways:
The distribution of silicon and aluminium along the tetrahedral sites mixed with the nature of the barium atom makes an impact on the surrounding silicate framework (Newham and Megaw,1960). The Si-Al bonds are partially ordered, and in some cases the aluminium substitute’s silicon.
The order in celsian is very simple, each aluminium tetrahedron is surrounded by four silicon tetrahedra, and vice versa (Newham and Megaw,1960). Also there is another type of transformation besides aluminium-silicon, where silicon-poor goes into a silicon-rich network that involves having to simultaneously be a replacement of Al, and Si at other sites.
The barium ion has an irregular configuration close to the one in potassium in the feldspars. Each barium has an oxygen close, and thanks to this configuration it has a strong effect on the silicon-oxygen-silicon bond angles.
The order of increasing stability is paracelsian→hexacelsian→celsian in a temperature range between 500 °C to the 1000 °C.
As temperature rises from the 1,600 °C to 1,760 °C it goes from celsian to a reversible form of hexacelsian. Paracelsian is less stable than the other two and celsian is the most stable.
is poorly developed, except on coarse crystals. Eighteen crystal forms have been identified; eleven of them coincide with those known for orthoclase. Observed twining includes manebach twins on (001) and baveno twins on (021). Some samples of celsian were found to have a rare lamellar twinning (Spencer, 1941).
The density is about 3.31 to 3.33 g/cm³. This might be the case due to some impurities in the structure of the mineral. It has a hardness of 6 on the Moh's scale, this hardness is due to the short length of the bond in the structure, since is relative short tends to be harder.
Celsian has very attractive features such as chemical stability and high mechanical resistance, which can be favourably exploited in order to obtain enhanced-performance composites with respect to bulk glass. (Cannillo, Carlier, Manfredini, Montorsi, and Siligardi 2006).
Many studies shows that by increasing the amount of celsian phases in the glasses results in increased bulk of crytaslization.(Khater and Idris, 2004)
Feldspar
Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....
mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...
, barium aluminosilicate, Ba
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
Al
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
2Si
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
2O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
8. The mineral occurs in contact metamorphic rock
Metamorphic rock
Metamorphic rock is the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...
s with significant barium
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
content. Its crystal system
Crystal system
In crystallography, the terms crystal system, crystal family, and lattice system each refer to one of several classes of space groups, lattices, point groups, or crystals...
is monoclinic, and it is white, yellow, or transparent in appearance. In pure form, it is transparent. Synthetic barium aluminosilicate is used as a ceramic
Ceramic
A ceramic is an inorganic, nonmetallic solid prepared by the action of heat and subsequent cooling. Ceramic materials may have a crystalline or partly crystalline structure, or may be amorphous...
in dental fillings
Dental fillings
This page is about types of dental restorative materials. For dental fillings see dental restorationsDental restorative materials are specially fabricated materials, designed for use as dental restorations , which are used to restore tooth structure loss, usually resulting from but not limited to...
and other applications.
The mineral is named after Anders Celsius
Anders Celsius
Anders Celsius was a Swedish astronomer. He was professor of astronomy at Uppsala University from 1730 to 1744, but traveled from 1732 to 1735 visiting notable observatories in Germany, Italy and France. He founded the Uppsala Astronomical Observatory in 1741, and in 1742 he proposed the Celsius...
.
Composition
Celsian is a barium feldspar with a chemical composition BaAl2Si2O8. It forms part of the feldspar group and belongs to the celsian-hyalophaneHyalophane
Hyalophane or jaloallofane is a crystalline mineral with chemical formula [AlSi2O8] and a hardness of 6 – 6½. It is part of the feldspar group of tectosilicates, and is considered a barium-rich potassium feldspar...
series and the celsian-orthoclase
Orthoclase
Orthoclase is an important tectosilicate mineral which forms igneous rock. The name is from the Greek for "straight fracture," because its two cleavage planes are at right angles to each other. Alternate names are alkali feldspar and potassium feldspar...
series. It has some resemblance to anorthite
Anorthite
Anorthite is the calcium endmember of plagioclase feldspar. Plagioclase is an abundant mineral in the Earth's crust. The formula of pure anorthite is CaAl2Si2O8.-Mineralogy :...
, and it has four distinct polymorphs
Polymorphism (materials science)
Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements...
.
The essential elements are Si,Al,O and Ba. Some common impurities in the mineral are Fe, Ti, Mg, K and Ca. Celsian is stable from room temperature up to 1590 °C ( Lin and Foster,1968). The most common trace elements are potassium and calcium, in an analysis of the approximate chemical composition of celsian the following wt% were found:
• SiO2—35.1
• Al2O3---26.8
• BaO----35.8
• K2O-----2.3
Total:100.0 (Newham and Megaw,1960).
Geologic occurrence
Celsian is of limited occurrence. Most of the barium feldspars are associated with exhalative hydrothermal processes and low-and medium-grade metamorphism (Moro and Cembranos and Fernandez, 2001). It is also associated with sedimentary and meta sedimentary rocks, manganese, ferromanganese and barite deposits.Celsian can be found in places like Wales, Zamora (Spain), Alaska, California, Sweden and Japan, also with hendricksite on the Franklin mines in New Jersey.
Structure
The symmetry in celsian is somewhat different from the symmetry normally found in feldspars. It is monoclinic with a body centered lattice similar to those of anorthite. Insufficient evidence has been found to suggest that celsian lacks a center of symmetry, so its space group is I 2/c (Newnham and Megaw, 1960). The space group differs from others of its group like orthoclase, albite and body center anorthite are C2/m, C1bar and I1bar.X-ray analysis shows that the values for the lattice parameters a, b, c axes and angles are approximately a=863 pm, b=131.0 pm, c=1400 pm and β=116°, θ=90° (Gay, 1956).
There are 8 formula units per cell, and the general position is eightfold, so all atoms can lie in general positions (Newnham and Megaw,1960). This structure is very similar to that of orthoclase and sanidine but differs in a couple of ways:
- 1. The distribution of Si and Al.
- 2. The coordinates of all the atoms.
The distribution of silicon and aluminium along the tetrahedral sites mixed with the nature of the barium atom makes an impact on the surrounding silicate framework (Newham and Megaw,1960). The Si-Al bonds are partially ordered, and in some cases the aluminium substitute’s silicon.
The order in celsian is very simple, each aluminium tetrahedron is surrounded by four silicon tetrahedra, and vice versa (Newham and Megaw,1960). Also there is another type of transformation besides aluminium-silicon, where silicon-poor goes into a silicon-rich network that involves having to simultaneously be a replacement of Al, and Si at other sites.
The barium ion has an irregular configuration close to the one in potassium in the feldspars. Each barium has an oxygen close, and thanks to this configuration it has a strong effect on the silicon-oxygen-silicon bond angles.
Polymorphism of celsian
There are four distinctive polymorphs of celsian, two of them are the natural minerals and the other two are synthetic products. The first are paracelsian and celsian, the second ones are hexacelsian and the other one is related to the mineral cymrite (Lin and foster, 1967).The order of increasing stability is paracelsian→hexacelsian→celsian in a temperature range between 500 °C to the 1000 °C.
As temperature rises from the 1,600 °C to 1,760 °C it goes from celsian to a reversible form of hexacelsian. Paracelsian is less stable than the other two and celsian is the most stable.
Twinning
Barium feldspars occur in optically uniform crystals where the twinningCrystal twinning
Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations. A twin boundary or composition surface separates the two crystals....
is poorly developed, except on coarse crystals. Eighteen crystal forms have been identified; eleven of them coincide with those known for orthoclase. Observed twining includes manebach twins on (001) and baveno twins on (021). Some samples of celsian were found to have a rare lamellar twinning (Spencer, 1941).
Physical properties
Celsian shows a c(001) perfect cleavage and a b(010) good cleavage, which marks the difference with its polymorph paracelsian which has a [110] indistinct cleavage. There are different crystals habits like adularia, larger, stout crystals (Spencer, 1941), and long, slender to acicular. It is usually colorless and transparent with a pearly to non-fluorescent luster.The density is about 3.31 to 3.33 g/cm³. This might be the case due to some impurities in the structure of the mineral. It has a hardness of 6 on the Moh's scale, this hardness is due to the short length of the bond in the structure, since is relative short tends to be harder.
Optical properties
Some other optical properties are the 2V angle which is approximately 88° with a maximum birefringence of 0.014, biaxial with a negative sign (Newnham and Megaw, 1960). It has a moderate relief.Uses
The uses of celsian are mostly related to glass and ceramics. This uses are usually achieved by the preparation of pure synthetic monoclinic celsian.Celsian has very attractive features such as chemical stability and high mechanical resistance, which can be favourably exploited in order to obtain enhanced-performance composites with respect to bulk glass. (Cannillo, Carlier, Manfredini, Montorsi, and Siligardi 2006).
Many studies shows that by increasing the amount of celsian phases in the glasses results in increased bulk of crytaslization.(Khater and Idris, 2004)