A-spodumene

In the LAS-matrix system matrix cracks parallel to the fibre axis were observed at ATc = 800°C, accompanied by a reduction in Young s modulus, although flexure strength seemed to remain unaffected by thermal shock treatment. This was attributed to the difference in the direction of matrix crack propagation in the two composites due to the formation of a-spodumene-... 

The deformation microstructures of monoclinic pyroxenes are considered in Section 9.9.2. Optical microscope observations (Griggs, Turner, and Heard 1960 Raleigh 1965) indicate that the dominant slip system in monoclinic pyroxenes is also (100)[100]. However, van Duysen and Doukhan (1984) found by TEM that in naturally deformed a-spodumene the activated slip systems are (110) [001] and [lT0) <110>. In specimens of a-spodumene deformed by scratching, they also observed interesting microstructures of dislocations and faults that may be related to the twins observed in deformed diopside by Kirby and Christie (1977). 

Dislocations and faults in deformed monoclinic a-spodumene and diopside. Van Duysen and Doukhan (1984) examined the dislocations in both naturally and experimentally deformed single crystals of a-spodumene. The naturally deformed specimens were characterized by a heterogeneous distribution of dislocations (p 10 cm ). The dislocations are not dissociated and most have b = [001] and lie in the crystallo-graphically equivalent planes (110) and (iTO). Other dislocations, probably with b = [110] and [TlO], were also observed and commonly interact to form irregular networks according to the reaction... 

Figure 9.32. WBDF image of the dislocations and faults on (100) observed in a (110) scratched foil of a-spodumene. (From van Duysen and Doukhan 1984.)...

Figure 9.33. WBDF images of the dislocations and faults in a-spodumene observed with several different diffraction vectors.

Figure 9.34. Diagram showing a (100) microtwin one unit cell wide in a-spodumene projected onto (010).

If the faults observed by van Duysen and Doukhan (1984) in scratched a-spodumene are microtwins with R = j[001], as suggested, then they would be out-of-contrast for all g = hkA. However, since images with these reflections are not given, the microtwin model caimot be adequately tested... 

Duysen, J. C. van, Doukhan, J. C. (1984). Room temperature microplasticity of a-spodumene LiAlSi206. Phys. Chem. Minerals, 10, 125-32. 

Bend Test. See modulus of rupture. Beneficiation. US term for any process, or combination of processes, for increasing the concentration of a mineral in an ore the term is now replacing the older term mineral dressing in the UK. An example of beneficiation in the ceramic industry is the treatment of certain pegmatites to produce a SPODUMENE (q.v.) concentrate. 

At least the petalite conversion aspect of this data appears to be confirmed in some deposits, since after the entire pegmatite was solidified much of the petalite appeared to have been transformed into spodumene and quartz, and occasionally some eucryptite and quartz. The spodumene was in the form of psuedomorphs after petalite, and its very low iron content was similar to that of petalite, and much lower than that of most primary spodumene. However, this phase data and these reactions do not appear to have general applicability, since (1) solid phase reactions do not occur without the solid being remelted or dissolved, at least on a molecular scale, and then recrystallized after the reaction has taken place. (2) The data shows 3-spodumene being stable at 680°C, whereas at atmospheric pressure the change in form from a to 3-spodumene only occurs in ore concentrates above about 1000°C. Also, P-spodumene has never been found in a lithium deposit, and a-spodumene s melting point is shown as 700°C compared to its atmospheric value of 1423°C. (3) Changes in pressure normally have only a relatively minor effect upon a solid s... 

Log-shaped white crystals. SQI is a spodumene, quartz and feldspar mixture resulting from the decomposition of petalite and feldspar white crystals. Grey or white crystals. 

Rhodonite MnSiOs (often with considerable Ca) a-spodumene LiAlSi20e... 

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