Ephesite is a rare member of the mica

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, silica (silicon dioxide, ) is usually consid ...

group,

phyllosilicate 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 ...

. It is restricted to

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 ...

-free, alumina rich mineral assemblages and has been found in

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...

n deposits in the

Postmasburg Postmasburg is a town in the Northern Cape province of South Africa. Location The Town is located approximately 170 km east of Upington. The town is north of Griquatown and west-south-west of Daniëlskuil. History Originally a station o ...

district as well as Ephesus,

Turkey Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a transcontinental country located mainly on the Anatolian Peninsula in Western Asia, with a small portion on the Balkan Peninsula in ...

.Phillips, F. (1931) ''Ephesite (soda-maragrite) from the Postmasburg district, South Africa,'' Corpus Christi College, Cambridge, pp. 482-485

Composition

Ephesite has an ideal

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbol ...

of NaLiAl₂(Al₂Si₂)O₁₀(OH)_2.Rieder, M. et al. (1998) Nomenclature of the Micas. The Canadian Mineralogist, 36, 41-48 Ephesite and

paragonite Paragonite is a mineral, related to muscovite. Its empirical formula is . A wide solvus separates muscovite from paragonite, such that there is little solid solution along the vector Na+ K+ and apparent micas of intermediate composition is most ...

are closely related due to their substitution of

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 ...

in place of

potassium Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosph ...

. The general form of most micas, which can vary such as in the place of ephesite, can be written as W(X,Y)_2-3Z₄O₁₀(OH,F)₂ as observed by many sources. In the case of ephesite the W compound is sodium and the (X,Y) is

lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid ...

and

aluminium Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...

, it also bears two

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 ...

s as the end members.

Structure

Ephesite, a mica structure, arises from the stacking of T-O-T layers along the c-axis direction connected by I-cations where T,O, and I stand for tetrahedral-, octahedral-, and interlayer. Creating long, flat sheets of sodium and lithium rich tetrehedra. Ephesite in particular belongs in the trioctahedral mica subgroup. Micas are determined and named for their end members and species that define a wide range of compositions. Depending on the interlayer cation, the micas are subdivided into true micas (if 50% I cations present are monovalent) or brittle micas ( if > 50% I cations present are divalent). Ephesite with monovalent cations of Na prove to be a true mica and with 2.5 octahedral cations are trioctahedral. Ephesite is classified as an uncommon true non-K mica of which only 2.1% of the micas are categorized.

Physical properties

Ephesite found in its natural state is translucent and pink in color. It has a vitreous luster and pearly on the cleavages. Categorized as a

triclinic 180px, Triclinic (a ≠ b ≠ c and α ≠ β ≠ γ ) In crystallography, the triclinic (or anorthic) crystal system is one of the 7 crystal systems. A crystal system is described by three basis vectors. In the triclinic system, the crystal i ...

crystal system In crystallography, a crystal system is a set of point groups (a group of geometric symmetries with at least one fixed point). A lattice system is a set of Bravais lattices. Space groups are classified into crystal systems according to their poin ...

and belongs with the point group 1 symmetry elements, this crystal class includes a one-fold rotation with or without inversion. As a group the micas are characterized by their perfect basal cleavage, giving thin, flexible, and elastic cleavage plates. Crystals are usually tabular with prominent basal planes and hexagonal in outline. Ephesite has been found as 2M1 and 1M polytype series and shows perfect cleavage on the axis.Mason, B. and L. Berry (1968) Elements of Mineralogy. W.H. Freeman and Company, 2, print

History

The history of study of the mineral ephesite begins with its first appearance in Ephesus, Asia Minor at Gumach Dagh in a deposit also associated with emery discovered by J. Lawrence Smith in 1851. I. Lea in 1867 had discovered a mineral of the same composition which he had been calling under a different name, lesleyite. Later, ephesite was closely compared to a mineral

margarite Margarite is a calcium rich member of the mica group of the phyllosilicates with formula: Ca Al2(Al2 Si2) O10(O H)2. It forms white to pinkish or yellowish gray masses or thin laminae. It crystallizes in the monoclinic crystal system. It typical ...

which shared the same composition as ephesite with a substituted Ca for Na. Many times ephesite will be referred to as a soda-margarite for this substitution of sodium. Because of these findings the names ephesite, lesleyite, soda-margarite and potash-margarite have been used synonymously. Derivation of the name ephesite comes from its place of occurrence, Ephesus.

References

{{Phyllosilicates Phyllosilicates Triclinic minerals Monoclinic minerals Minerals in space group 1 Minerals in space group 15