Howlite

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Howlite
Howlite-122859.jpg
kidney howlite (size: 4.1 × 2.5 × 2.5 cm) from Wentworth, Hants County, Nova Scotia, Canada
General and classification
chemical formula Ca 2 [B 3 O 4 (OH) 2  • OSiB 2 O 4 (OH) 3 ]
Mineral class
(and possibly department) 		Borates (formerly: Silicates and Germanates)
System no. to Strunz
and to Dana 		6.CB.20 ( 8th edition : VIII / F.28)
03/25/05/01
Similar minerals Magnesite
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic 2 / m
Space group P 2 1 / c
Lattice parameters a  = 12.82  Å ; b  = 9.35 Å; c  = 8.61 Å
β  = 104.8 °
Formula units Z  = 4
Physical Properties
Mohs hardness 3 to 3.5
Density (g / cm 3 ) measured: 2.53 to 2.59; calculated: 2.61
Cleavage Well
Break ; Tenacity uneven
colour colorless, white, beige
Line color White
transparency transparent to translucent
shine Glass gloss, earthy matt
Crystal optics
Refractive indices n α  = 1.583 to 1.586
n β  = 1.596 to 1.598
n γ  = 1.600
Birefringence δ = 0.017
Optical character biaxial negative
Axis angle 2V = measured: 60 to 90 °; calculated: 88 °
Pleochroism not known
Other properties
Special features can only be distinguished from magnesite by chemical analysis

Howlite is a rarely occurring mineral from the mineral class of " borates " (formerly: "silicates and germanates", see classification ). It crystallizes in the monoclinic crystal system with the chemical composition Ca 2 [B 3 O 4 (OH) 2  • OSiB 2 O 4 (OH) 3 ] and develops mostly bulbous, kidney-shaped and massive aggregates that are either colorless or white to beige in color. Howlite also rarely develops tabular crystals that show a glassy sheen on the crystal surfaces.

Howlite is only processed into gemstones .

Etymology and history

Howlite was first found in Brookville near Windsor (Canada) and described in 1868 by James Dwight Dana , who named the mineral after the Canadian chemist, geologist and mineralogist Henry How (1828–1879).

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the howlite belonged to the mineral class of "silicates and germanates" and there to the department of "chain silicates and band silicates (inosilicates)".

The 9th edition of Strunz's mineral systematics, which has been in effect since 2001 and is used by the IMA, assigns howlite to the now independent class of " borates " and there in the department of "triborates". This department is, however, further subdivided according to the structural structure, so that the mineral is classified in the sub-department “Chains and Band (Ino) -Triborate "can be found, where it is the only member of the unnamed group 6.CB.20 .

The systematics of minerals according to Dana assigns the howlite to the common class of "carbonates, nitrates and borates" and there in the department of "anhydrous borates with hydroxyl or halogen". There he is the only member of the unnamed group 25.03.05 within the sub-section “ Anhydrous borates with hydroxyl or halogen ”.

Crystal structure

Howlite crystallizes monoclinically in the space group P 2 1 / c with the lattice parameters a  = 12.82  Å ; b  = 9.35 Å; c  = 8.61 Å and β = 104.8 ° as well as 4 formula units per unit cell .

properties

Howlite is often traversed by brown-black veins, which in their marbling resemble the coveted matrix of turquoise . The crystal surfaces show a glass luster, whereas the fracture surfaces are matt. Howlite breaks shell-like like glass .

Howlite is very similar in appearance to magnesite (a magnesium carbonate) and can often only be distinguished from it by chemical analysis. Howlite "melts" under the action of hydrochloric acid to form a kind of gel , whereas magnesite reacts by developing gas. Determining the density to distinguish the two is often not sufficient, as howlite with a density of 2.5 to 2.6 g / cm³ is very similar to magnesite (2.9 to 3.1 g / cm³). In addition, magnesite is often even lighter due to air inclusions. 

Education and Locations

Rare large crystalline formation of howlite on anhydrite (size: 3.5 × 3.3 × 2.6 cm) from Cape Breton Island, Canada

Howlith formed hydrothermally and is most prevalent in Borat - deposits to be found. There he appears in paragenesis with colemanite , ulexite and bakerite, among others .

Howlith has so far (as of 2010) been found at around 30 sites worldwide. In addition to its type locality Brookville near Windsor, it was found in Canada on Cape Breton Island . In Germany it appeared at Kohnstein (Thuringia) and Rehden (Lower Saxony), among others .

Furthermore, howlite could be found at the sites of Mesa del Almo near Aguja and in the borate deposit near La Salada (Tubutama) in the state of Sonora in Mexico; Bela Stena in Serbian in the Belgrade district ; Gemerská Poloma (Okres Rožňava, Košice) in Slovakia; " Bigadiç Mine" can be found in the Turkish province of Balıkesir and in several regions of the US states of California and Nevada .

use

As a gem

Howlite as a gemstone, 96ct
Turquoise imitation made of blue colored howlite

Howlite is a popular gemstone , but due to its low Mohs hardness of 3 to 3.5, it is very soft and must therefore be protected from damage by stabilization (coating made of resin or plastic) to protect it against daily use .

Manipulations and imitations

Since magnesite looks so similar to howlite, but is more common and therefore cheaper, it is often wrongly sold as howlite. However, both of them, colored blue, serve as imitations of the rare and valuable matrix turquoise .

Esoteric

In esotericism , howlite is said to have a special psychological and physical effect, for which there is, however, no scientific evidence.

Among other things, it should strengthen judgment and memory, reduce stress, feelings of pain and anger, neutralize negative energies and release blockages. Howlite water is said to have a generally positive effect on problems with bones, teeth, joints and nails.

See also

literature

  • Paul Ramdohr , Hugo Strunz : Klockmann's textbook of mineralogy . 16th edition. Ferdinand Enke Verlag, 1978, ISBN 3-432-82986-8 , pp. 686 .
  • Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag GmbH, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 209 .
  • Walter Schumann: Precious stones and gemstones. All species and varieties in the world. 1600 unique pieces . 13th revised and expanded edition. BLV Verlags GmbH, Munich et al. 2002, ISBN 3-405-16332-3 , p. 224 .

Web links

Commons : Howlite  - collection of images, videos, and audio files

Individual evidence

  1. ↑ Webmineral - Howlite
  2. ↑ a b c d Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 344 .
  3. ↑ a b c d e Howlite at mindat.org (engl.)
  4. ↑ Bernhard brother embellished stones . Neue Erde Verlag, 1998, ISBN 3-89060-025-5