Foitite

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Foitite
Foitite, quartz, orthoclase.jpg
General
Category Mineral
IMA symbol Foi [1]
Crystal system Trigonal
Identification
Mohs scale hardness7

Foitite is a mineral in the tourmaline group, [2] it is a vacancy-dominant member of the group. [3] Foitite is in the 'vacancy' group, due to the absence of atoms in the X site. [2]

Contents

According to the Czech Geological Society, foitite is rare. [4] However foitite is quite common among low-temperature tourmalines [5] and it might be more common than previously thought. [6]

The color of the mineral is dark indigo with purple tints to bluish-black. [3]

Name

The mineral was named in 1993 by D. J. MacDonald, Frank C. Hawthorne, and Joel D.Grice after Franklin F. Foit, Jr. [5]

Chemistry

It lacks alkalis like sodium. [7]

Foitite is a member of the tourmaline mineral group, which is a complex aluminum borosilicate. The chemical formula of foitite is (NaFe3+Al6)(Al6Si6O18)(BO3)3(OH)4.

In this formula, sodium [8] (Na) acts as the dominant cation, iron (Fe3+) replaces some of the aluminum (Al) in the crystal structure, and boron (B) replaces some of the silicon (Si) atoms. The BO3 groups are trigonal planar borate ions, and the OH groups represent hydroxyl ions.

The crystal structure of foitite consists of continuous chains of silicon-oxygen tetrahedra, with aluminum and boron ions substituting within these chains. The aluminum and boron substitutions create charge imbalances, which are compensated by the presence of sodium and iron ions.

Foitite typically forms in granitic rocks enriched in boron, such as pegmatites. It is commonly associated with other minerals such as quartz, feldspar, and muscovite. The presence of iron in foitite gives it a characteristic black color.

Occurrence

It occurs in quartz veins [9] and possibly occurs in granite pegmatites. [10]

Its type locality is California. [5] Foitite has also been reported in Marquette County, Michigan. [6] It has been reported in Wales and it is predicted that a more widespread distribution of the mineral in Wales will be shown. [2]

Related Research Articles

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<span class="mw-page-title-main">Mineral</span> Crystalline chemical element or compound formed by geologic processes

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<span class="mw-page-title-main">Pegmatite</span> Igneous rock with very large interlocked crystals

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3
(PO
4
)
2
·8H
2
O
) is a hydrated iron phosphate mineral found in a number of geological environments. Small amounts of manganese Mn2+, magnesium Mg2+, and calcium Ca2+ may substitute for iron Fe2+ in the structure. Pure vivianite is colorless, but the mineral oxidizes very easily, changing the color, and it is usually found as deep blue to deep bluish green prismatic to flattened crystals. Vivianite crystals are often found inside fossil shells, such as those of bivalves and gastropods, or attached to fossil bone. Vivianite can also appear on the iron coffins or on the corpses of humans as a result of a chemical reaction of the decomposing body with the iron enclosure.

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References

  1. Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi: 10.1180/mgm.2021.43 . S2CID   235729616.
  2. 1 2 3 "Mineral Database - Mineralogy of Wales". National Museum Wales. Retrieved 2021-10-12.
  3. 1 2 "Foitite gemstone information". www.gemdat.org. Retrieved 2021-10-28.
  4. Journal of Geosciences. Czech Geological Society. 2010. p. 17.
  5. 1 2 3 "Foitite". www.mindat.org. Retrieved 2021-10-12.
  6. 1 2 "Foitite" (PDF). The A. E. Seaman Mineral Museum. Retrieved 29 October 2021.
  7. "Wisconsin Geological & Natural History Survey » Foitite". wgnhs.wisc.edu. Retrieved 2021-10-14.
  8. UNIVERSITY of WISCONSIN–MADISON. "Foitite".
  9. "Tourmaline-Bearing Quartz Veins in the Baraboo Quartzite, Wisconsin: Occurrence and Significance of Foitite and "Oxy-Foitite"". CiteSeerX   10.1.1.615.277 .
  10. "Foitite" (PDF). Mineral Data Publishing. 2001. Retrieved 29 October 2021.