Chayesite
| Chayesite | |
|---|---|
 |
|
| General and classification | |
| chemical formula | KMg 4 Fe 3+ Si 12 O 30 |
|
Mineral class (and possibly department) |
Silicates and germanates - ring silicates |
|
System no. to Strunz and to Dana |
9.CM.05 ( 8th edition : VIII / E.22) 63.02.01a.02 |
| Similar minerals | Cordierite , Osumilite , Roedderite |
| Crystallographic Data | |
| Crystal system | hexagonal |
| Crystal class ; symbol | dihexagonal-dipyramidal; 6 / m 2 / m 2 / m |
| Space group | P 6 / mcc (No. 192) |
| Lattice parameters | a = 10.153 Å ; c = 14.388 Å |
| Formula units | Z = 2 |
| Frequent crystal faces | {0001}, {10-12}, {11-20}, {10-10} |
| Physical Properties | |
| Mohs hardness | not determined |
| Density (g / cm 3 ) | calculated: 2.68 |
| Cleavage | no |
| colour | dark blue to colorless |
| Line color | White |
| transparency | transparent |
| shine | Glass gloss |
| Crystal optics | |
| Refractive indices |
n ω = 1.575 n ε = 1.578 |
| Birefringence | δ = 0.003 |
| Optical character | uniaxial positive |
| Pleochroism | strong: dark blue - colorless |
The mineral chayesite is a very rare ring silicate from the milarite group with the idealized chemical composition K Mg 4 Fe 3+ Si 12 O 30 . It crystallizes in the hexagonal crystal system and develops deep blue or tabular crystals, usually less than a millimeter in size, colored by hematite .
Chayesite is found in the finely crystalline matrix of lamproites and in foreign rock inclusions in basaltic magmas. In addition to its type locality , a Lamproit from Moon Canyon , Utah , USA , Chayesite has so far only been detected in a few other locations: In Lamproit from Cancarix , Spain and in foreign rock inclusions in basaltic magmas from Ettringer Bellerberg in the Vulkaneifel , Germany , the Pauliberg in Burgenland , Austria and Mont Denise in Auvergne , France .
Etymology and history
Chayesit was discovered in 1986 by Christiane Wagner and Danielle Velde in Lamproit by Moon Canyon, Utah and initially referred to as the roedderite- like phase . A more detailed investigation three years later led to the description of the new mineral chayesite as a vacancy (□) -Fe 3+ analog of roedderite. It was named after the petrologist and former president of the "Mineralogical Society of America" Dr. Felix Chayes.
classification
In the outdated, but still partially common 8th edition of the mineral classification by Strunz Chayesit belongs Almarudit , Armenit , Berezanskit , Brannockit , Darapiosit , Dusmatovit , Emeleusit , Faizievit , Merrihueit , Oftedalit , Osumilith , Osumilith- (Mg) , Poudretteit , Roedderit , Sogdianite , sugilite and yagiite to the general division of " ring silicates (cyclosilicates)" in the " milarite-osumilite group " with system no. VIII / E.22 .
The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also classifies chayesite in the "ring silicates" section. This is, however, further subdivided according to the structure of the rings, so that the mineral can be found in the sub-section "[Si 6 O 18 ] 12− -six double rings" according to its structure . Therein it is part of Agakhanovit-Ce , Almarudit, Armenit, Berezanskit, Brannockit, Eifelit , Darapiosit, Dusmatovit, Friedrichbeckeit , Klöchit , Merrihueit, Milarit, Oftedalit, Osumilith, Osumilith- (Mg), Poudretteit, Roedderit, Trattnerit , Shibkovit , Sogdianit, Sugilite and Yagiite to the " milarite group " with the system no. 9.CM.05 .
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the chayesite to the class of "silicates and germanates", but there in the more finely divided division of "ring silicates: condensed rings". Here it is in the " Milarite Osumilith Group (Milarite Osumilith Subgroup) " with the system no. 63.02.01a can be found in the subsection “ Ring Silicates : Condensed, 6-membered Rings”.
Chemism
Chayesite is the □ -Fe 3+ end link of a mixed crystal kingdom from Roedderite to Chayesite, which is responsible for the exchange reactions
- [B] Na + [T2] Mg 2+ = [B] □ + [T2] Fe 3+
underlying.
The measured composition from the type locality is [C, B] (K 1.14 Na 0.1 ) [A, T2] (Mg 3.29 Fe 2+ 0.96 Mn 2+ 0.04 Fe 3+ 0.64 Ti 0.03 Al 0.04 ) [T1] [Si 12 O 30 ], the positions in the crystal structure being indicated in square brackets .
Crystal structure
Chayesite crystallizes in the hexagonal crystal system in the space group P 6 / mcc (space group no.192 ) with the lattice parameters a = 10.153 Å and c = 14.388 Å as well as two formula units per unit cell .
Chayesite is isotypic to milarite , i.e. H. it crystallizes with the same structure as milarite.
The T1 position, which builds up the double rings, contains only silicon (Si 4+ ).
The 12-fold coordinated C position is fully occupied with potassium and some sodium, the 9-fold coordinated B position is empty or contains only small amounts of Na. The T2 position contains magnesium and up to 1 apfu (atoms per formula unit) iron, the octahedral A position is almost completely occupied with magnesium with small amounts of iron.
Education and Locations
Chayesite forms at very high temperatures around 1000 to 1100 ° C and low pressure under oxidizing conditions and has been documented in two different occurrences (as of 2016).
In lamproites , chayesite occurs in the finely crystalline matrix of these igneous rocks, where they are deposited directly from the potassium-rich melt in the late phase of crystallization. This type includes the type locality , a lamproit from Moon Canyon , Utah , USA , where chayesite occurs together with olivine , clinopyroxene , phlogopite , K- Richterite , potassium feldspar , apatite , ilmenite , pseudobrookite Cr- spinel and glass . In a lamproit from an outcrop near Sierra de las Cabras, near Cancarix , Spain , chayesite occurs with aegirine , apatite, rutile and calcite as well as dalyite .
In addition to these igneous deposits, chayesite is also formed during the contact metamorphosis of low-aluminum xenolites in basaltic magmas . This type includes the three other documented sites on Ettringer Bellerberg in the Vulkaneifel , Germany , on Pauliberg in Burgenland , Austria and on Mont Denise in Auvergne , France .
See also
Web links
- Mineral Atlas: Chayesite (Wiki)
Individual evidence
- ↑ a b c d e f g h i j k l m n o p q r s t u v w x D. Velde, O. Medenbach, C. Wagner, W. Schreyer: Chayesite, K (Mg, Fe2 +) 4Fe3 + [Si12O30]: A new rock-forming silicate mineral from the osumilite group from the Moon Canyon (Utah) lamproite . In: American Mineralogist . tape 74 , 1989, pp. 1368–1373 ( available online at minsocam.org [PDF; 489 kB ; accessed on March 9, 2019]).
- ↑ Mindat - example of a crystal group made of blue chayesite
- ^ A b c d e E. Alietti, MF Brigatti, S. Capredi AND L. Poppi: The roedderite-chayesite series from Spanish lamproites: crystal-chemical characterization . In: Mineralogical Magazine . tape 58 , December 1994, p. 655–662 ( available online at rruff.info [PDF; 556 kB ; accessed on March 9, 2019]).
- ↑ a b Mindat - type locality Caspar quarry, Bellerberg volcano, Ettringen, Mayen, Eifel, Rhineland-Palatinate, Germany
- ^ A b Karl Ettinger, Walter Postel, Josef Taucher, Franz Walter: Minerals of the Osumilith group (Roedderit, Merrihueit, Chayesit and Osumilith) from the Styrian-Burgenland volcanic area, Austria . In: Tschermaks mineralogical and petrographic communications . tape 31 , 1996, pp. 215–234 ( PDF on ZOBODAT [accessed March 9, 2019]).
- ↑ a b Mindat - type locality Basalt quarry, Pauliberg, Kobersdorf, Oberpullendorf, Burgenland, Austria
- ↑ a b Mindat - type locality Mont Denise, Espaly-Saint-Marcel, Le Puy-en-Velay, Haute-Loire, Auvergne, France
- ↑ a b c C. Wagner, D. Velde: The mineralogy of K-richterite-bearing lamproite . In: American Mineralogist . tape 71 , 1986, pp. 17–37 ( available online at minsocam.org [PDF; 2.5 MB ; accessed on March 9, 2019]).