Labradorite

Labrador-isieren, n. play of colors (as on lab-radorite), iridescence, -stein, m. Labrador stone, labradorite. 

The zeolite, scolecite, the feldspar, labradorite, and the ultra-marine, hackmanite, gave high-strength cements but all were much affected by water - the strength of the labradorite cement disappeared almost entirely - possibly because of the presence of free acid. 

Ti 30-60 ppm Occasionally high concentrations (up to 600-700 ppm) in intermediate members of plagioclase series (labradorite bytownite). 

Feldspars are the most abundant minerals in the earth s crust, accounting for about 60% of all igneous rocks. They are derivatives of silica in which about one-half or one-quarter of the silicon atoms have been replaced by aluminum. Feldspar is used in the manufacture of certain types of glass and pottery. Some feldspar crystals, such as moonstone (white perthilte), Amazon stone (green microcline), and multicolored labradorite, are used as gem stones and in architectural decorations. Some are used as a coating and filler in the production of paper. 

Nearly all silicates contain some sodium, and there are several silicates which contain relatively large quantities—e.g. soda felspar or albite the soda-lime felspars —e.g. labradorite sodalite nepheline analcime lapis lazuli etc. 

Microcline, albite and labradorite were obtained from Ward s Canada Limited. Cleaved crystal fragments and 60 mesh-sized samples were ultrasonically cleaned prior to use. Powdered samples (particle size < 25 ym) were prepared by grinding in a tungsten carbide ball mill, wet-sieving and washing in water. 

Cesium-ion concentrations in distilled water and synthetic ground-waters were measured after contact with the feldspars for various periods of time, over the temperature range 150°C to 200°C. It was found that for short reaction times (< 5 days), there was little reduction in the concentration of cesium ion, i.e. little sorption of Cs+ by the minerals. Removal of Cs+ from solution was enhanced by increased mineral surface area, reaction temperature and time. It was observed that in the extreme case for powdered labradorite, 98% of an initial 10 2 mol dm 3 solution of Cs+ was sorbed after 14 days at 200°C in distilled water. The morphology, composition and chemical structure of the mineral surfaces were investigated by several analytical methods, as described below. 

FTIR Spectra. After reaction, the mineral samples were subjected to ultrasonic treatment in acetone for periods of up to 1 hour. Transmission IR spectra of the released product fines from reactions of 60-mesh labradorite and microcline with 10 2 mol dm 3 CsCl in distilled water at 150 C for 47 days are presented in Figure 3. The spectrum obtained from of the labradorite reaction product (Figure 3(a)) is identical with that of a sample of natural pollucite (Figure 3(c)). The spectrum obtained from the microcline reaction product (Figure 3(b)) contains bands in the 500 cm""1 to 800 cm"1 region, due to unreacted microcline, in addition to the major bands of pollucite. Heating the samples overnight at 105 C resulted in the disappearance of the water absorption bands at about 3500 cm 1 and 1680 cm 1. 

Figure 1. SEM photomicrographs of microcline (a, c and d), albite (b) and labradorite (e-g) after hydrothermal reaction with CsCl (see text).

Figure 3. FTIR spectra of (a) fines removed ultrasonically from 60-mesh labradorite (see text) (b) fines removed ultrasonically from 60-mesh microcline (see text) (c) natural pollucite.

Plagioclase feldspars Albite, oligoclase, andesine, labradorite, bytownite, anorthite... 

Figure 5.22 Polarized absorption spectra of iron in plagioclase feldspar (from Hofmeister Rossman, 1983). (a) Visible region spectra with peaks originating from Fe3+ ions in tetrahedral coordination (b) near-infrared spectra attributed to Fe2+ ions in the Ca sites. The labradorite, from Rabbit Hills, Oregon, contains about 0.1 wt per cent Fe203 and 0.3 wt per cent FeO. (Crystal thickness 1.0 cm.)...

Nash, D. B. Conel, J. E. (1974) Spectral reflectance systematics for mixtures of powdered hypersthene, labradorite, and ilmenite. J. Geophys. Res., 79,1615-21. 

Play of color is the term used to describe the internal spectral colors that appear inside some specimens of materials like opal and some synthetics. The colors seem to move when the specimen is turned or the light source is moved. Labradorescence is a broad play of colors common in labradorite and other minerals (mostly feldspars) having polysynthetic twinning. 

All of these minerals are used in ceramics and refractories, and labradorite is sometimes used as a building stone. 

Nissen et al. (1973) and Cliff et al. (1976) found that the composition of the two types of lamellae in a labradorite (An54) differed by at least 12 percent An. 

Beran A. (1987) OH groups in nominally anhydrous framework structures an infrared spectroscopic investigation of danburite and labradorite. Phys. Chem. Mineral. 14, 441-445. 

Release of trace elements such as strontium from feldspar is also observed to be nonstoichio-metric (Brantley et al, 1998). At pH 3, bytownite, microcline, and albite aU release strontium at an initially fast rate that slows to near stoichiometric values at steady state. In addition, aqueous strontium is enriched in Sr compared to the bulk mineral early in dissolution. All feldspars smdied evenmally released strontium in isotopic abundance roughly equal to that of the bulk mineral. Nonstoichiometric release of strontium was explained by the presence of defects or accessory phases in the minerals. Taylor et al. (2000) also reported that the initial dissolution of labradorite was nonstoichiometric during dissolution in column reactors with inlet solution pH 3, but that the mineral dissolved and released strontium stoichiometrically at steady state. In contrast to the earlier work, however, Sr/ Sr in solution did not differ from that of the bulk labradorite during dissolution in the column experiments. 

---