Pyroxenes are an extensive group of chain silicates . Many pyroxenes are rock-forming minerals .
Content
- 1 Classification
- 2 Structure
- 3 Genesis
- 3.1 Being in space
- 4 Application
- 5 Literature
- 6 notes
- 7 References
Classification
Pyroxenes are divided into rhombic ( orthopyroxenes ) and monoclinic ( clinopyroxenes ).
| Minerals | The composition of the minals | Main staff | Group |
|---|---|---|---|
| I. Mg-Fe pyroxenes | |||
| 1. Enstatitis (En) | Mg 2 Si 2 O 6 | (Mg, Fe) 2 Si 2 O 6 | Pbca |
| 2. Ferrosilite (Fs) | Fe 2 Si 2 O 6 | ||
| 4. Clinoferrosilite | (Mg, Fe) 2 Si 2 O 6 | P2 / c | |
| 5. Dude | (Mg, Fe, Ca) 2 Si 2 O 6 | P2 / c | |
| II. Mn-Mg Pyroxenes | |||
| 6. Donpikorit | (Mn, Mg) MgSi 2 O 6 | Pbca | |
| 7. Kanoit (Ka) | MnMgSi 2 O 6 | P21 / c | |
| III. Ca Pyroxenes | |||
| 8. Diopside (Di) | CaMgSi 2 O 6 | Ca (Mg, Fe) Si 2 O 6 | C2 / c |
| 9. Gedenbergit (Hd) | CaFe 2+ Si 2 O 6 | ||
| 10. Augitus | (Ca, Mg, Fe) 2 Si 2 O 6 | C2 / c | |
| 11. Johansenite (Jo) | CaMnSi 2 O 6 | C2 / c | |
| 12. Petedunite (Pe) | CaZnSi 2 O 6 | C2 / c | |
| 13. Esseniitis (Es) | CaFe 3+ AlSiO 6 | C2 / c | |
| IV. Ca-Na pyroxenes | |||
| 14. Omphacite | (Na, Ca, Mg) (Mg, Fe, Al) Si 2 O 6 | C2 / c P2 / n | |
| 15. Aegirine-augite | C2 / c | ||
| V. Na Pyroxenes | |||
| 16. Jadeite (Jd) | NaAlSi 2 O 6 | Na (Al, Fe 3+ ) Si 2 O 6 | C2 / c |
| 17. Aegirine (Ae) | NaFe 3+ Si 2 O 6 | ||
| 18. Cosmochlor (Ko) | NaCr 3+ Si 2 O 6 | C2 / c | |
| 19. Jervisit (Je) | NaS 3+ Si 2 O 6 | C2 / c | |
| VI. Li pyroxenes | |||
| 20. Spodumene | LiAlSi 2 O 6 | C2 / c | |
Structure
The main motive for the structure of pyroxenes is the chains of SiO 4 tetrahedra extended along the c axis. In pyroxenes, tetrahedra in chains are alternately directed in different directions. In other chain silicates, the chain repeatability period is usually longer.
There are two nonequivalent positions in the structure - M1 and M2. The M1 position is close in shape to the regular octahedron and there are small cations in it. The M2 position is less correct and when large cations (especially Ca) enter it, it acquires the 8th coordination , silicon-oxygen chains shift relative to each other, and the mineral structure becomes monoclinic .
Genesis
Pyroxenes are extremely common minerals. They make up about 4% of the mass of the continental crust. In the oceanic crust and mantle, their role is much larger.
In surface conditions are unstable. With metamorphism, pyroxenes appear in the epidote-amphibolite facies. With increasing temperature, they are stable until the complete melting of the rocks. With increasing pressure, the composition of pyroxenes changes, but their role in rocks does not decrease. They disappear only at depths greater than 200 km.
Pyroxenes are found in almost all types of terrestrial rocks. One explanation for this fact is that the average composition of the earth's crust is close to that of augite pyroxene.
Being in space
Pyroxene is one of the main minerals of lunar regolith (along with olivine , anorthite and ilmenite ). The content of orthopyroxene and clinopyroxene in the soil sample delivered by the Hayabusa apparatus from the Itokawa asteroid is 11%. [one]
Application
The vast majority of pyroxenes is of no practical interest. Only spodumene is the main ore mineral of lithium , and some rare varieties of pyroxenes are used in jewelry and craftsmanship.
Most often, jadeite (incorrectly identified with jade similar to it) and jadeite rocks close to it are used to make jewelry. It was a sacred stone among some peoples of South America - Mayans, Aztecs and Olmecs.
Also used chrome diopside - bright green diopside with a small admixture of chromium . Chromdiopside is typical of mantle lherzolites and kimberlite pipes are an important source of this mineral. Another type of chrome diopside deposits is associated with pegmatoid segregations in dunites . A serious disadvantage of chrome diopside is its relatively low hardness. This significantly limits the use of this rare stone in jewelry. Sometimes diopsids of Slyudyanka are faceted, which have great collection value. In addition, rare star diopsides from southern India are highly regarded.
Literature
- Morimoto, Nobuo. 1989. Nomenclature of Pyroxenes. Canadian Mineralogist, 27, 143-156
- Nomenclature of pyroxenes N. Morimoto, J. Fabries, AK Ferguson, IV Ginzburg, M. Ross, FA Seifert, J. Zussman, K. Aoki, and G. Gottardi American Mineralogist; October 1988; v. 73; no. 9-10; p. 1123–1133