Staurolite

Kreuz-stein, m. cross-stone (chiastolite, harmo-tome, staurolite). -attick,n. crosspiece fourway cross(piece). -tisch, m. (Micros.) mechanical stage. 

Average of reported values for zircon, andalusite, silli-manite, staurolite, topaz, titanite, thortveitite, muscovite, apophyllite, hardystonite, analcite, carnegieite, sodalite, danburite, scapolite, and cristobalite mean deviation 0.02 A. 6 Average for BP04 (1.54 A.) and KHjPO, (1.56 A.). For KjSOi and other sulfates. i For Mg(C104)-6H,0. 

Statutes, tank facility, 24 304-305. See also Regulation Staurolite in coal, 6 718 Stayman apples, 73 33 Steady-state analysis... 

Mineral Bronzite Augite Augite Olivine Epidote Tourmaline Staurolite Actinolite Biotite, site 1 Biotite, site 2... 

Downing, K. H., Meisheng, H., Wenk, H. R., O Keefe, M. A. (1990) Resolution of oxygen atoms in staurolite by theee-dimensional transmission electron microscopy . Nature 348, 525-528. 

H-R Wenk, KH Downing, M Hu, MA O Keeefe. 3D structure determination from electron-microscope images electron crystallography of staurolite. Acta Cryst. A48 700-716,1992. 

In thermal metamorphism, biotite occurs in the clorite-sericite facies as a dispersed phase in the argillitic matrix and is stable up to low-grade cornubianites. In regional metamorphism, biotite is typical of argillitic and pelitic rocks up to the staurolite-garnet facies (biotite, biotite-sericite, biotite-chlorite, and albite-biotite schists, and garnet-staurolite micaschists). 

Wunder B, Meixner A, Romer RL, Feenstra A, Schettler G, Heinrich W (2007) Lithium isotope fractionation between Li-bearing staurolite, Li-mica and aqueous fluids an experimental study. Chem Geol 238 277-290... 

Well-known European localities are in Switzerland and Brittany and in the United States this mineral is common in the schists of New England, and those of the southern Alleghenies. Frequently the crystals are found loose in the soil after the disintegration of the country rock. The name staurolite is derived from the Greek meaning a cross, in reference to the twin crystals, the more nearly perfect crosses being somewhat in demand as curios. 

Figure 4.6 Polarized absorption spectra of staurolite.----------a spectrum —p spectrum -----y spectrum. The staurolite, containing 1.42 Fe2+ ions per formula unit, is...

Coordination symmetry of iron and cobalt in staurolite The crystal field spectra of Fe2+ ions surrounded by oxygen in regular octahedral sites normally contain absorption bands centred near 1,000 nm or 10,000 cm-1 (see fig. 3.2). By changing from octahedral to tetrahedral coordination, absorption bands for tetrahedral Fe2+ ions would, according to eq. (2.7), be predicted to occur at (% x 10,000) or 4,444 cm-1 (2,250 nm) if the iron-oxygen distances remain identical in the two coordinations. Tetrahedrally coordinated Fe2+ ions in spinel, MgAl204, for example, produce an absorption band near 4,830 cm"1 (2,070 nm) ( 5.3.3). 

The polarized spectra of lusakite, the cobaltian staurolite from Zambia (Cech et al., 1981), which are illustrated in fig. 4.7 together with (inset) the spectra of the hexahydrated Co2+ and tetrahedral Co2+ cations in spinel, show that Co2+ ions also occur in tetrahedral coordination in the staurolite structure. The profiles and intensities of the triple-peak absorption band between 500 nm and 650 nm are characteristic of tetrahedral Co2+ ions. 

The polarized spectra of staurolite, Fe2Al9Si4023(0H), accomodating tetrahe-drally coordinated Fe2+ ions (point symmetry Cm mean Fe-0 = 200.8 pm) and consisting of absorption bands spanning the 5,000 to 7,000 cm-1 region (Bancroft and Bums, 1967a Dickson and Smith, 1976), are illustrated in fig. 4.6 and discussed in 4.4.3. These bands completely mask any contributions from Fe2+ ions that might be present in centrosymmetric octahedral sites in the staurolite structure. The A, and CFSE parameters of tetrahedral Fe2+ ions in staurolite are estimated to be about 5,300 cm-1 and 3,700 cm-1, respectively. The spectra of the cobaltian staurolite, lusakite, illustrated in fig 4.7, indicates that tetrahedrally coordinated Co2+ ions have A, and CFSE values of about 6,500 cm-1 and 7,800 cm-1, respectively. 

When Co2+ ions occur in tetrahedral coordination, the ground-state becomes 4A2 4F), and spin-allowed transitions are to the 4T2(4F), 4TX(4F) and 47 (4P) states (fig. 3.12). Note that the 4A2 —> 4T2(4F) transition provides a direct measure of A,. When Co2+ ions are present in distorted tetrahedral sites, as in the cobaltian staurolite lusakite ( 4.4.3), each of the excited triplet crystal field states is resolved into several levels, so that numerous polarization-dependent absorption bands occur in the visible to near infra-red spectra (cf. fig. 4.7). 

Cech, F., Povondra, P. Vrana, S. (1981) Cobaltian staurolite from Zambia. Bull. Mineral., 104,526-9. 

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