Cesanite is the end member of the
apatite-
wilkeite-
ellestadite series that substitutes all of apatite's
phosphate
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid .
The phosphate or orthophosphate ion is derived from phosph ...
ions
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 conven ...
with
sulfate
The sulfate or sulphate ion is a polyatomic anion with the empirical formula . Salts, acid derivatives, and peroxides of sulfate are widely used in industry. Sulfates occur widely in everyday life. Sulfates are salts of sulfuric acid and many ...
ions and balances the difference in charge by replacing several
calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...
ions with
sodium
Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable ...
ions. Currently very few sites bearing cesanite have been found and are limited to a geothermal field in
Cesano,
Italy
Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...
from which its name is derived,
Măgurici Cave in
Romania
Romania ( ; ro, România ) is a country located at the crossroads of Central, Eastern, and Southeastern Europe. It borders Bulgaria to the south, Ukraine to the north, Hungary to the west, Serbia to the southwest, Moldova to the east, and ...
, and in the
San Salvador Island
San Salvador Island (known as Watling's Island from the 1680s until 1925) is an island and district of The Bahamas. It is widely believed that during Christopher Columbus's first expedition to the New World, this island was the first land h ...
cave
A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word ''cave'' can refer to smaller openings such as sea ...
s in the
Bahamas
The Bahamas (), officially the Commonwealth of The Bahamas, is an island country within the Lucayan Archipelago of the West Indies in the North Atlantic. It takes up 97% of the Lucayan Archipelago's land area and is home to 88% of the ar ...
.
History
Cesanite was first discovered in 1981 while the
Italian National Electricity Board was doing
exploratory drilling to examine a reservoir of heated
brine to determine its potential as a
geothermal energy source. When it was first found it was thought to be an apatite until after more thorough examination.
Structure
Cesanite was originally determined by Tazzoli (1983) to be
isotypic Isostructural chemical compounds have similar chemical structures. " Isomorphous" when used in the relation to crystal structures is not synonymous: in addition to the same atomic connectivity that characterises isostructural compounds, isomorphous ...
to that of
hydroxylapatite
Hydroxyapatite, also called hydroxylapatite (HA), is a naturally occurring mineral form of calcium apatite with the formula Ca5(PO4)3(OH), but it is usually written Ca10(PO4)6(OH)2 to denote that the crystal unit cell comprises two entities. ...
. This was determined by refining the original
unit cell
In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector, for example) does not necessaril ...
dimensions and comparing them to the atomic coordinates of Holly Springs hydroxylapatite. From this it was extrapolated that although different
elements are substituted for cesanite, the structure and cell parameters are nearly the same with some differences in the
bond length
In molecular geometry, bond length or bond distance is defined as the average distance between nuclei of two bonded atoms in a molecule. It is a transferable property of a bond between atoms of fixed types, relatively independent of the rest of ...
s of the
tetrahedra
In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the o ...
.
[Tazzoli V., (1983) The Crystal-structure of ceanite, CA1+XNA4-X(SO4)3(OH)X.(1-X)H2O, a sulfate isotypic to apatite. Mineralogical Magazine, 47, 59-63.] This similarity was to confirm the
space group
In mathematics, physics and chemistry, a space group is the symmetry group of an object in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of an object that leave it uncha ...
''P''3/m previously assigned to cesanite, this changed in 2002 after a reexamination of cesanite by Piotrowski et al. was prompted by its similarities to a synthetically produced
analog
Analog or analogue may refer to:
Computing and electronics
* Analog signal, in which information is encoded in a continuous variable
** Analog device, an apparatus that operates on analog signals
*** Analog electronics, circuits which use analog ...
. After this study it was found that the
crystal structure
In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric patterns ...
of cesanite to be
isostructural Isostructural chemical compounds have similar chemical structures. " Isomorphous" when used in the relation to crystal structures is not synonymous: in addition to the same atomic connectivity that characterises isostructural compounds, isomorphous ...
to this
synthetic analog with the chemical formula Ca
2Na
3 4)3">OH)(SO4)3 What can be inferred from this is that while hydroxylapatite remains similar in its chemical formula it is not longer to be considered a structural analog. The new correct space group is ''P''. It can be inferred that the reason the mistake went unnoticed for so long is that cesanite retains
pseudo-symmetry in the array of its tetrahedra that closely mimics ''P''3/m.
Cesanite's crystal structure is made up of tetrahedra of
sulfide 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 con ...
surrounded by
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
anions
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 conven ...
distributed along with
hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. I ...
ions around the Ca and Na ions occupying the M1 through four sites.
The M1 and M2 cites create distorted
pentagonal
In geometry, a pentagon (from the Greek πέντε ''pente'' meaning ''five'' and γωνία ''gonia'' meaning ''angle'') is any five-sided polygon or 5-gon. The sum of the internal angles in a simple pentagon is 540°.
A pentagon may be simpl ...
bipyramids
A (symmetric) -gonal bipyramid or dipyramid is a polyhedron formed by joining an -gonal pyramid and its mirror image base-to-base. An -gonal bipyramid has triangle faces, edges, and vertices.
The "-gonal" in the name of a bipyramid does no ...
while the M3 and M4 create tricapped
trigonal
In crystallography, the hexagonal crystal family is one of the six crystal families, which includes two crystal systems (hexagonal and trigonal) and two lattice systems (hexagonal and rhombohedral). While commonly confused, the trigonal crystal ...
prisms. The M3 and M4
polyhedra
In geometry, a polyhedron (plural polyhedra or polyhedrons; ) is a three-dimensional shape with flat polygonal faces, straight edges and sharp corners or vertices.
A convex polyhedron is the convex hull of finitely many points, not all on ...
share faces when they are next to each other and form columns parallel to
01while isolated sulfate tetrahedra alternate along the
c axis.
Physical properties
Cesanite veins are massive in habit and appear white in color with a silky luster. Individual crystals are colorless and transparent to translucent with a greasy luster. These crystals are elongated and begin with a pyramid on {101*0} that is distorted by a flatting that occurs down the length of the crystal which then extends down with two parallel faces until they are cut off by either a pinacoid or another pyramid.
According to the newest sources the unit-cell parameters of cesanite are ''a'' = 9.4630 and ''c'' = 6.9088 Å. In thin section cesanite remains transparent and has moderate
birefringence.
In addition to is structure at room temperature, cesanite exhibits different crystal structures at different temperatures. Polymorphs occur at 425, 625, and 740 °C. These different forms are cause by expansion along the crystallographic axises as cesanite is heated.
[Deganello S., Artioli G. (1982) Thermal expansion of cesanite between 22 °C and 390 °C. Nues jahrbuch für Mineralogie, Monatshefte, 12, 565-568.]
Geologic occurrence
Cesanite has been found in only three places to date. The original occurrence was observed as part of a
fracture sealing process where cesanite
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, macro ...
s grew to fill in the void. It was found growing in a loosely packed vein of small crystals that became intergrown with those of the neighboring
görgeyite crystals.
Further occurrences have been noticed in several caves. First in 2001 inside of Lighthouse Cave located on San Salvador Island filling in gaps in
corroded
Corroded is a heavy metal band from Ånge, Sweden. The band is best known for their song ''Time And Again'', which was the theme song for the Swedish 2009 ''Survivor'' television series on TV4. The band's second album ''Exit to Transfer'', rel ...
gypsum
Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywal ...
and in 2003 inside Măgurici Cave in Romania it was found in close association with
hydroxylapatite
Hydroxyapatite, also called hydroxylapatite (HA), is a naturally occurring mineral form of calcium apatite with the formula Ca5(PO4)3(OH), but it is usually written Ca10(PO4)6(OH)2 to denote that the crystal unit cell comprises two entities. ...
.
[Onac BP, Mylroie JE, White WB. (2001) Mineralogy of cave deposits on San Salvador Island, Bahamas. Carbonates and Evaporites, 16, 8-16.][Onac BP., Verdes DS. (2003) Sequence of secondary phosphates deposition in a karst environment: evidence from Măgurici Cave (Romania). European Journal of Mineralogy, 15, 741-745.] It has been presumed that in sequence hydroxylapatite is deposited followed by the formation of cesanite when the solution in which the crystals are being formed is rich in sodium and sulfate and depleted of calcium.
See also
*
Beraunite
References
External links
Introduction to Uniaxial Minerals
Calcium minerals
Sodium minerals
Sulfate minerals
Hexagonal minerals
Minerals in space group 174