Danburite

Danburite is a mineral from the mineral class of " silicates and Germanates ", which may be abundant in various localities in part, but overall is not widespread. It crystallizes in the orthorhombic crystal system with the chemical composition Ca [ B2Si2O8 ] and usually develops prismatic to columnar crystals to about 50 cm in length, but also granular or massive mineral aggregates.

Reiner Danburit is transparent and colorless. But it may also appear white and accept by various foreign admixtures a gray, greenish, reddish, yellowish or brownish color by multiple refraction due to lattice defects or multicrystalline training, the transparency decreases accordingly. His stroke color, however, is always white. Visible crystal faces have a glass - like sheen to bold, massive aggregates, however, are rather dull.

With a Mohs hardness 7 to 7.25 Danburit one of the hard and minerals is as the reference mineral quartz is able to scratch the window glass. Danburit shows only an indistinct cleavage along { 001 } and an uneven to conchoidal weak, brittle fracture.

Special Features

Before the blowpipe phosphoresces Danburit and slowly melt to a white, bubbly, translucent glass. With borax it melts with effervescence to a translucent pearl. Add powdered state, Danburite decomposes slowly in hydrochloric acid.

Etymology and history

Danburite was discovered in Danbury, Fairfield County in the U.S. state of Connecticut and described in 1839 by Charles Upham Shepard, who named the mineral after its type locality.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the Danburit belonged to the mineral class of " silicates and Germanates " and then to the Department of " framework silicates ( tectosilicates ) ", where he formed a distinct group with Reedmergnerit.

The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the Danburit also in the class of " silicates and Germanates " there, however, in the newly defined division of the " framework silicates ( tectosilicates ) without zeolitic H2O " one. This department is also further divided according to the possible presence of other anions, so that the mineral is found according to its composition in the subsection " framework silicates ( tectosilicates ) without additional anions " where there. Than namesake of the " Danburitgruppe " with the system no Forms 9.FA.65 and the other members Maleevit and Pekovit.

The mainly common in English-speaking classification of minerals according to Dana assigns the Danburit in the class of " silicates and Germanates " there, however, in the department of " group silicates: Si2O7 Groups and O, OH, F, and H2O" one. Here it is also named the " Danburitgruppe " with the system no. ": With Si2O7 Si2O7 Groups and O, OH, F, and H2O with borate groups silicates group " to find 56.03.01 within the subdivision of.

Education and Locations

Danburit formed by hydrothermal processes in pegmatite cavities as well as in mining and alpinotype transitions. But it can also occur in metamorphic skarns. Accompanying minerals include albite, anhydrite, Apophyllite, Axinit, Bakerit, calcite, Datolith, dolomite, fluorite, gypsum, grossular, quartz, stilbite, titanite and various micas and tourmalines.

Overall, Danburite has so far (as of 2011) are detected in over 120 localities. Apart from its type locality Danbury, Connecticut, the mineral in the United States was still in Clarke County, Alabama, at Port Clarence in Alaska, on Maude Hill in Cochise County, Arizona, in Iberville Parish, Louisiana, at Stratton in Texas, in San Juan County and at Gold Hill ( Tooele County), at Green Mountain in King County in Washington and in several places in the U.S. states of California, Montana, and New York.

In Germany the mineral previously occurred in Hildfeld and Silbach in Sauerland (NRW ) and Staßfurt in Saxony -Anhalt. In Austria, the mineral has been on Scheiblingkirchen ditch near Bad Gastein and Kötschachtal found ( a part of the Gastein Valley ), and Switzerland were found, among other things in the Val Cadlimo in the canton of Ticino, in Etzlital in the canton of Uri, and at several locations in the canton of Grisons.

Other localities lie include Afghanistan, Australia, Bolivia, China, France, Iran, Italy, Japan, Canada, Madagascar, Mexico, Myanmar, Namibia, Nepal, Norway, Romania, Russia, Slovakia, Tajikistan, Tanzania, Czech Republic, Turkmenistan, the United Kingdom ( UK) and in Vietnam.

Crystal structure

Danburit crystallizes in the orthorhombic space group Pnam ( Raumgruppen-Nr. 62) with the lattice parameters a = 8.04 Å; b = 8.75 Å and c = 7.73 Å and four formula units per unit cell.

Use

Although Danburit may look very similar with good quality depending on the color different gemstones such as, among others, the Phenakit, quartz (especially the variety citrine ) or the topaz and can be sanded also good because of its high hardness and low splitting tendency, it is only occasionally as gemstone used. His great sensitivity to heat as they arise eg during soldering of grasping in jewelry and would bring the stone to melt quickly, making it a difficult -to-handle stone.