Hexagonite

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Hexagonite
Tremolite-172420.jpg
General
Categorymineral variety of tremolite
Formula
(repeating unit)		 Ca 2 Mg 5 (Si 8 O 22) (OH)2
Space group monoclinic – prismatic
Identification
Colorred to pink, lilac to purple
Crystal habit elongated, bladed crystals, granula
Twinning simple, multiple
Cleavage [110] perfect; [010] distinct
Fracture uneven
Tenacity brittle
Mohs scale hardness5.0–6.0
Luster vitreous
Refractive index 1.599–1.637 biaxial ( - )
Birefringence 0.019–0.028
Pleochroism bluish–red, deep rose, deep red–violet
Dispersion weak, r < v

Hexagonite is the red to pink, lilac to purple manganoan variety of tremolite. A rare amphibole, it can be transparent, translucent, and rarely opaque.

Manganese Chemical element with atomic number 25

Manganese is a chemical element with symbol Mn and atomic number 25. It is not found as a free element in nature; it is often found in minerals in combination with iron. Manganese is a metal with important industrial metal alloy uses, particularly in stainless steels.

Tremolite Amphibole, double chain inosilicate mineral

Tremolite is a member of the amphibole group of silicate minerals with composition: ☐Ca2(Mg5.0-4.5Fe2+0.0-0.5)Si8O22(OH)2. Tremolite forms by metamorphism of sediments rich in dolomite and quartz. Tremolite forms a series with actinolite and ferro-actinolite. Pure magnesium tremolite is creamy white, but the color grades to dark green with increasing iron content. It has a hardness on Mohs scale of 5 to 6. Nephrite, one of the two minerals of the gemstone jade, is a green variety of tremolite.

Amphibole double chain inosilicates

Amphibole is an important group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain SiO
4 tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Amphiboles can be green, black, colorless, white, yellow, blue, or brown. The International Mineralogical Association currently classifies amphiboles as a mineral supergroup, within which are two groups and several subgroups.

Contents

Properties

Hexagonite is pleochroic, potentially displaying varying shades of blue, violet, purple, or red. [1] It is also known as "mangan-tremolite", since the manganese imparts the mineral's unique colors.[ citation needed ] Pink, lilac, and purple are the most common colors. [1] Hexagonite has been successfully faceted. [1]

Chemical formulae and history

Tremolite was discovered in 1789. [2] Hexagonite, a varietal form of tremolite, has a Mohs hardness of 5.0-6.0. [3] Like tremolite, it is a calcium magnesium silicate hydroxide with the formula: Ca 2 Mg 5 (Si 8 O 22) (OH)2. [3]

Calcium Chemical element with atomic number 20

Calcium is a chemical element with 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 to its heavier homologues strontium and barium. It is the fifth most abundant element in Earth's crust and the third most abundant metal, after iron and aluminium. The most common calcium compound on Earth is calcium carbonate, found in limestone and the fossilised remnants of early sea life; gypsum, anhydrite, fluorite, and apatite are also sources of calcium. The name derives from Latin calx "lime", which was obtained from heating limestone.

Magnesium Chemical element with atomic number 12

Magnesium is a chemical element with symbol Mg and atomic number 12. It is a shiny gray solid which bears a close physical resemblance to the other five elements in the second column of the periodic table: all group 2 elements have the same electron configuration in the outer electron shell and a similar crystal structure.

Silicate class of chemical compounds, salts and esters of silicic acids

In chemistry, a silicate is any member of a family of anions consisting of silicon and oxygen, usually with the general formula [SiO(4−2x)−
4−x]
n, where 0 ≤ x < 2. The family includes orthosilicate SiO4−
4, metasilicate SiO2−
3, and pyrosilicate Si
2O6−
7. The name is also used for any salt of such anions, such as sodium metasilicate; or any ester containing the corresponding chemical group, such as tetramethyl orthosilicate.

The mineral was given the name, hexagonite, because its crystal structure was believed at one time to be hexagonal. Since then, however, it has been found to be monoclinic. [3]

Crystal structure Ordered arrangement of atoms, ions, or molecules in a crystalline material

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 that repeat along the principal directions of three-dimensional space in matter.

Occurrence

The mineral is found primarily in the Balmat-Edwards zinc district of Edwards, St. Lawrence County, New York, United States. [4] It was also found in the Czech Republic in the Chýnov caves. [5]

Edwards, New York Town in New York, United States

Edwards is a town in St. Lawrence County, New York, United States. The population was 1,156 at the 2010 census. The village is named after Edward McCormack, brother of the founder.

St. Lawrence County, New York County in the United States

St. Lawrence County is a county in the U.S. state of New York. As of the 2010 census, the population was 111,944. The county seat is Canton. The county is named for the Saint Lawrence River, which in turn was named for the Christian saint Lawrence of Rome, on whose Feast day the river was discovered by French explorer Jacques Cartier.

Related Research Articles

Beryl gemstone: cyclosilicate

Beryl ( BERR-əl) is a mineral composed of beryllium aluminium cyclosilicate with the chemical formula Be3Al2Si6O18. Well-known varieties of beryl include emerald and aquamarine. Naturally occurring, hexagonal crystals of beryl can be up to several meters in size, but terminated crystals are relatively rare. Pure beryl is colorless, but it is frequently tinted by impurities; possible colors are green, blue, yellow, red (the rarest), and white. Beryl is also an ore source of beryllium.

Topaz Silicate mineral

Topaz is a silicate mineral of aluminium and fluorine with the chemical formula Al2SiO4(F, OH)2. Topaz crystallizes in the orthorhombic system, and its crystals are mostly prismatic terminated by pyramidal and other faces. It is one of the hardest naturally occurring minerals (Mohs hardness of 8) and is the hardest of any silicate mineral. This hardness combined with its usual transparency and variety of colors means that it has acquired wide use in jewellery as a cut gemstone as well as for intaglios and other gemstone carvings.

Tourmaline cyclosilicate mineral group

Tourmaline is a crystalline boron silicate mineral compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is classified as a semi-precious stone and the gemstone comes in a wide variety of colors.

Garnet mineral, semi-precious stone

Garnets are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives.

Violet (color) color

Violet is the color at the end of the visible spectrum of light between blue and the invisible ultraviolet. Violet color has a dominant wavelength of approximately 380-450 nanometers. Light with a shorter wavelength than violet but longer than X-rays and gamma rays is called ultraviolet. In the color wheel historically used by painters, it is located between blue and purple. On the screens of computer monitors and television sets, a color which looks similar to violet is made, with the RGB color model, by mixing red and blue light, with the blue twice as bright as the red. This is not true violet, for it does not match the color of a single wavelength shorter than that of blue light.

Fluorite mineral, calcium fluoride

Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon.

Actinolite amphibole, double chain inosilicate mineral

Actinolite is an amphibole silicate mineral with the chemical formula Ca2(Mg4.5-2.5Fe2+0.5-2.5)Si8O22(OH)2.

Onyx Banded variety of the mineral chalcedony

Onyx primarily refers to the parallel banded variety of the silicate mineral chalcedony. Agate and onyx are both varieties of layered chalcedony that differ only in the form of the bands: agate has curved bands and onyx has parallel bands. The colors of its bands range from white to almost every color. Commonly, specimens of onyx contain bands of black and/or white. Onyx, as a descriptive term, has also been applied to parallel banded varieties of alabaster, marble, obsidian and opal, and misleadingly to materials with contorted banding, such as "Cave Onyx" and "Mexican Onyx".

Jadeite Pyroxene mineral

Jadeite is a pyroxene mineral with composition NaAlSi2O6. It is monoclinic. It has a Mohs hardness of about 6.5 to 7.0 depending on the composition. The mineral is dense, with a specific gravity of about 3.4.

Erythrite arsenate mineral

Erythrite or red cobalt is a secondary hydrated cobalt arsenate mineral with the formula (Co3(AsO4)2·8H2O). Erythrite and annabergite (Ni3(AsO4)2·8H2O) (nickel arsenate) form a complete series with the general formula (Co,Ni)3(AsO4)2·8H2O.

Pezzottaite cyclosilicate mineral

Pezzottaite, marketed under the name raspberyl or raspberry beryl, is a newly identified mineral species, first recognized by the International Mineralogical Association in September 2003. Pezzottaite is a caesium analogue of beryl, a silicate of caesium, beryllium, lithium and aluminium, with the chemical formula Cs(Be2Li)Al2Si6O18. Named after Italian geologist and mineralogist Federico Pezzotta, pezzottaite was first thought to be either red beryl or a new variety of beryl ("caesium beryl"); unlike actual beryl, however, pezzottaite contains lithium and crystallizes in the trigonal crystal system rather than the hexagonal system.

Hardystonite sorosilicate mineral

Hardystonite is a rare calcium zinc silicate mineral first described from the Franklin, New Jersey, U.S. zinc deposits. It often contains lead, which was detrimental to the zinc smelting process, so it was not a useful ore mineral. Like many of the famous Franklin minerals, hardystonite responds to short wave ultraviolet light, emitting a fluorescence from dark purple to bright violet blue. In daylight, it is white to gray to light pink in color, sometimes with a vitreous or greasy luster. It is very rarely found as well formed crystals, and these are usually rectangular in appearance and rock-locked.

Anthophyllite amphibole, double chain inosilicate mineral

Anthophyllite is an amphibole mineral: ☐Mg2Mg5Si8O22(OH)2 (☐ is for a vacancy, a point defect in the crystal structure), magnesium iron inosilicate hydroxide. Anthophyllite is polymorphic with cummingtonite. Some forms of anthophyllite are lamellar or fibrous and are classed as asbestos. The name is derived from the Latin word anthophyllum, meaning clove, an allusion to the most common color of the mineral.

Stichtite hydrotalcite group mineral

Stichtite is a mineral, a carbonate of chromium and magnesium; formula Mg6Cr2CO3(OH)16·4H2O. Its colour ranges from pink through lilac to a rich purple colour. It is formed as an alteration product of chromite containing serpentine. It occurs in association with barbertonite (the hexagonal polymorph of Mg6Cr2CO3(OH)16·4H2O), chromite and antigorite.

Pabstite is a barium tin titanium silicate mineral that is found in contact metamorphosed limestone. It belongs to the benitoite group of minerals. The chemical formula of pabstite is Ba(Sn,Ti)Si3O9. It is found in Santa Cruz, California. The crystal system of the mineral is hexagonal.

Piemontite epidote supergroup, sorosilicate mineral

Piemontite is a sorosilicate mineral in the monoclinic crystal system with the chemical formula Ca2(Al,Mn3+,Fe3+)3(SiO4)(Si2O7)O(OH). It is a member of the epidote group.

Kanoite is a light pinkish brown silicate mineral that is found in metamorphic rocks. It is an inosilicate and has a formula of (Mg,Mn2+)2Si2O6. It is a member of pyroxene group and clinopyroxene subgroup.

Leucophoenicite nesosilicate mineral

Leucophoenicite is a mineral with formula Mn7(SiO4)3(OH)2. Generally brown to red or pink in color, the mineral gets its name from the Greek words meaning "pale purple-red". Leucophoenicite was discovered in New Jersey, US and identified as a new mineral in 1899.

References

  1. 1 2 3 Hexagonite Gemstone Information; Gem Data website; accessed August 2016
  2. ↑ Tremolite on Mindat.org
  3. 1 2 3 Hexagonite on Mindat.org
  4. ↑ Balmat Hexagonite; article; July 27, 2015; Fred Haynes blog; "WCGMC Activity;" accessed Aug 2017
  5. ↑ Litochleb J, Sejkora J (2007) Occurrence of tremolite-hexagonite in dolomite marbles in the Chýnov cave (southern Bohemia). Minerál 15: 124-126 (in Czech)


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