Stilbite

• Desmin

Stilbite (also desmin or Blätterzeolith ) is a collective name for the two minerals Stilbite - Ca and Stilbite -Na.

Both minerals are the mineral class of " silicates and Germanates " and form the end members of a mixed series with the chemical compositions:

• Stilbite - Ca: NaCa4 ( Si27Al9 ) O72 • 28 H2O
• Stilbite - Na: NA9 ( Si27Al9 ) O72 • 28 H2O

Stilbite crystallize in the monoclinic crystal system and develop mostly transparent to translucent, prismatic or tabular crystals, as well as complex penetration twins and sheaf -like mineral aggregates, which are either colorless or white, yellowish, pinkish to reddish and brown color. Also granular to massive aggregates are known

Special Features

Both end members show only small differences in the optical properties:

Stilbite are only sparingly soluble in hydrochloric acid.

Etymology and history

Stilbite was discovered in 1756 by Axel Frederic CRONSTEDT and described in 1796 by René -Just Haiiy and named after the Greek word " Stilbe " for shine because of its strong glass - to permuttartigen luster on the cleavage surfaces.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz Stilbite - Ca and Stilbite -Na belonged to the department of " framework silicates ( tectosilicates ), with zeolites " where they together with Barrerit, brewsterite - (Ba), brewsterite - ( Sr), epistilbite, Goosecreekit, heulandite (Ba), heulandite (Ca ), heulandite ( K), heulandite (Na ), heulandite - ( Sr), clinoptilolite (Ca), clinoptilolite (K ), clinoptilolite (Na) and Stellerit the subgroup " Blätterzeolithe I" with the system no. VIII/J.23 formed within the zeolite group.

The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns Stilbite - Ca and Stilbite -Na also in the department of " framework silicates ( tectosilicates ) with zeolitic H 2 O; Family of zeolites " one. This division, however, is further subdivided according to the type of binding form of scaffolding, so that the two minerals are " structural units with 4-4-1-1 boards " to find according to their composition in the subdivision where they without other members of the unnamed group 9. GE.10 form.

The mainly common in English-speaking classification of minerals according to Dana assigns the Stilbite in the department of " framework silicates: Zeolite - group " field. Here they are along with heulandite -Ca, heulandite -Na, heulandite -K, heulandite -Sr, Ba heulandite - clinoptilolite -K, clinoptilolite -Na, clinoptilolite - Ca, Stellerit and Barrerit in the group " heulandite and related species " with system no. Find 77.01.04 within the sub-division of "real zeolites ".

Education and Locations

Stilbite formed by hydrothermal processes in bubble chambers in volcanic rocks ( basalts and basaltic tonsil stones ), ore deposits or inputs or near thermal springs, but also in sedimentary rocks and are often found in paragenesis with Cavansit, Apophyllite and calcite, as well as with various other zeolites.

Stilbite -Ca has been at 146 localities (as of 2009 ) can be detected and is thus much more common than stilbite -Na, which has been detected at 14 localities.

Locations for Stilbite -Ca include Bertrix in Belgium; Santa Catarina in Brazil; Bavaria, Lower Saxony, Saxony and Thuringia in Germany; France; England, Northern Ireland and Scotland in the United Kingdom; Nova Scotia and Quebec in Canada; India; several regions in Italy; Styria and Tyrol in Austria; the regions of the Urals and East Siberia in Russia; Sweden; Switzerland; Bohemia and Moravia in the Czech Republic; Ukraine; Hungary; and many regions in the United States.

Locations for Stilbite -Na include South Australia and Victoria in Australia; India; Piedmont and Sardinia in Italy; as well as some regions of the United States.

Morphology

The crystals of the style bits often have a characteristic, sheaf -like appearance with the apparent orthorhombic { 010 } combinations, {100 } or {111 }. In fact, however, is monoclinic crossing twins in ( 010 ) and ( 001).

Structure

Both Stilbite crystallize in the monoclinic crystal system, space group C2 / m ( Raumgruppen-Nr. 12) with the lattice parameters a = 13.63 Å; b = 18.17 Å; c = 11.31 Å and β = 129.17 ° and one formula unit per unit cell.

Similar to the Heulandite the formula units of the style bits are linked to form a skeleton. When Stilbite this is, however, parallel to the c axis of channels with ten -membered rings parallel to the a axis and eight- membered rings.