Moganite is an

oxide mineral The oxide mineral class includes those minerals in which the oxide anion (O2−) is bonded to one or more metal alloys. The hydroxide-bearing minerals are typically included in the oxide class. The minerals with complex anion groups such as the si ...

with the

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 symbols, ...

Si O₂ (

silicon dioxide Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

) that was discovered in 1976. It was initially described as a new form of silica from specimens found in the Barranco de Medio Almud, in the municipality of

Mogán Mogán is a town and a Spanish municipality in the southwestern part of the island of Gran Canaria, which is one of the three main islands making up the Province of Las Palmas in the Canary Islands, Spain. Its population is (2013),

on the island of Gran Canaria, in the

Canary Islands The Canary Islands (; es, Canarias, ), also known informally as the Canaries, are a Spanish autonomous community and archipelago in the Atlantic Ocean, in Macaronesia. At their closest point to the African mainland, they are west of Morocc ...

(

Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = ''Plus ultra'' (Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , i ...

), receiving in a later work the name derived from this locality. In 1994 the International Mineralogical Association decided to disapprove it as a valid mineral, since it was considered indistinguishable from quartz. Subsequent studies allowed the IMA to rectify it in 1999, accepting it as a mineral species. It has the same

chemical composition A chemical composition specifies the identity, arrangement, and ratio of the elements making up a compound. Chemical formulas can be used to describe the relative amounts of elements present in a compound. For example, the chemical formula for ...

as quartz, but a different

crystal structure In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystal, crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric pat ...

. In 1994, the

International Mineralogical Association Founded in 1958, the International Mineralogical Association (IMA) is an international group of 40 national societies. The goal is to promote the science of mineralogy and to standardize the nomenclature of the 5000 plus known mineral species. Th ...

(IMA) had disapproved it as being a separate mineral because it was not clearly distinguishable from quartz. In 1999, however, moganite was approved as a valid mineral by the CNMNC, the Commission on New Minerals, Nomenclature and Classification (part of the IMA). Its IMA number is (CNMMN, No. 99-035). This mineral has been mainly found in dry locales such as Gran Canaria and

Lake Magadi Lake Magadi is the southernmost lake in the Kenyan Rift Valley, lying in a catchment of faulted volcanic rocks, north of Tanzania's Lake Natron. During the dry season, it is 80% covered by soda and is well known for its wading birds, including f ...

. It has been reported from a variety of locations in Europe, India and the United States. Physically, it has a

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

of about 6, a dull luster and appears as a semitransparent gray in color.

Structural information

The main

infrared spectroscopy Infrared spectroscopy (IR spectroscopy or vibrational spectroscopy) is the measurement of the interaction of infrared radiation with matter by absorption, emission, or reflection. It is used to study and identify chemical substances or function ...

(IR) differences between moganite and α-quartz occur in the

wavenumber In the physical sciences, the wavenumber (also wave number or repetency) is the ''spatial frequency'' of a wave, measured in cycles per unit distance (ordinary wavenumber) or radians per unit distance (angular wavenumber). It is analogous to temp ...

region below 650 cm⁻¹. Above this wavenumber, the frequencies of Si–O stretching vibrations of moganite are almost identical to those of quartz. Additional moganite bands were recorded near 165, 207, 296, 343, 419, 576, and 612 cm⁻¹.

Structural phase transition

Synchrotron A synchrotron is a particular type of cyclic particle accelerator, descended from the cyclotron, in which the accelerating particle beam travels around a fixed closed-loop path. The magnetic field which bends the particle beam into its closed p ...

X-ray powder diffraction data for moganite from has revealed a reversible

phase transition In chemistry, thermodynamics, and other related fields, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states of ...

from space group I2/a to Imab at approximately . The in-situ

Fourier transform infrared spectroscopy Fourier-transform infrared spectroscopy (FTIR) is a technique used to obtain an infrared spectrum of absorption or emission of a solid, liquid, or gas. An FTIR spectrometer simultaneously collects high-resolution spectral data over a wide spectr ...

shows that while the thermal responses of H₂O and OH in moganite display similarities to agate, the spectra are not completely identical. Absorptions in the O–H stretching region reveal that

dehydration In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mil ...

and

dehydroxylation In chemistry, hydroxylation can refer to: *(i) most commonly, hydroxylation describes a chemistry, chemical process that introduces a hydroxyl group () into an organic compound. *(ii) the ''degree of hydroxylation'' refers to the number of OH gr ...

is a multistage process. Although hydrogen loss starts below , hydrous species may well remain in moganite even at .

References

Monoclinic minerals Minerals in space group 15 Oxide minerals Silica polymorphs Silicon compounds {{silicate-mineral-stub