The approximate maximum and minimum amounts of any phase in a complex mineral mixture can be determined by solving a linear programming problem involving chemical mass balance and X-ray powder diffraction (XRD) data. The chemical information necessary is the bulk composition of the mixture and an estimation of the compositional range of each of the minerals in the mixture. Stoichiometric constraints for the minerals may be used to reduce their compositional variation. If only a partial chemical analysis for the mixture is available, the maximum amounts of the phases may still be estimated; however, some or all of the stoichiometric constraints may not apply. XRD measurements (scaled using an internal standard) may be incorporated into the linear programming problem using concentration-intensity relations between pairs of minerals. Each XRD constraint added to the linear programming problem, in general, reduces the difference between the calculated maximum and minimum amounts of each phase. Because it is necessary to define weights in the objective function of the linear programming problem, the proposed method must be considered a model. For many mixtures, however, the solution is relatively insensitive to the objective function weights.

An example consisting of a mixture of montmorillonite, plagioclase feldspar, quartz, and opal-cristobalite illustrates the linear programming approach. Chemical information alone was used to estimate the mineral abundances. Because quartz and opal-cristobalite are not chemically distinct, it was only possible to determine the sum, quartz + opal-cristobalite, present in the mixture.

Low-charge beidellites were synthesized by a hydrothermal treatment applied to an amorphous gel phase in basic solution. The hydrothermal conditions for the syntheses were chosen from the stability field of beidellite previously investigated in the literature. The synthetic samples were characterized chemically and structurally using X-ray diffraction, infrared spectroscopy, cation exchange capacity measurement, and chemical and thermal analyses. We compared the synthetic sample with a natural beidellite sample (SbId) from Idaho, USA, looking at chemical composition and particle size. The main difference is the octahedral site occupancy (cis- or trans-vacant layer structure). The natural SbId sample has trans-vacant layers and the synthetic sample has a preferentially cis-vacant character. This character can be modulated, using specific synthesis conditions. The cis- or trans-vacant layer structure of various synthetic beidellites was investigated at low temperature (<350°C) and pressure (<25 MPa). Depending on the pressure and/or synthesis temperature, the proportion of cis-vacant layers ranges from 20 to 100% and increases with the layer-charge deficit.

Twelve nontronites and two ferruginous smectites have been characterized with respect to Fe3+ occupancy of tetrahedral sites. The techniques used were near infrared, Fe-K X-ray absorption near-edge and X-ray absorption fine-structure spectroscopies, along with two X-ray diffraction techniques. The results show that calculations of the structural formulae of many nontronites should be adjusted to include Fe3+ in tetrahedral sites. The nontronite from Spokane County, Washington, (∼44% Fe2O3) is essentially an end-member with its non-siliceous tetrahedral sites occupied by Fe3+. Samples with chemical compositions similar to Garfield nontronite (∼36.5% Fe2O3) may have small amounts (<5% of total Fe3+) of tetrahedral Fe3+. Tetrahedral Fe3+ is unlikely to be present in samples containing less than ∼34% Fe2O3.

Two phlogopite, two mixed-layer phlogopite-vermiculite, and two vermiculite samples collected from the Palabora Complex of South Africa have been investigated at 295 K by X-ray diffraction, chemical analysis, and Mössbauer spectroscopy. In addition the temperature dependence of the Mössbauer spectra has been measured between 95 and 295 K for one phlogopite and one mixed-layer sample. The results of the chemical analyses and the Mössbauer spectra improve our knowledge of the vermiculitization process in the Palabora Complex. Both techniques indicate oxidation of the Fe ions during the sequence: phlogopite → mixed-layer → vermiculite. Further, the Mössbauer spectra indicate that Fe oxidation occurs mainly in the octahedral sites and suggest that migration and oxidation of the Fe2+ ions from the octahedral sites to the tetrahedral sites may occur during the transformation of phlogopite into a mixed-layer phase. Finally, the vermiculitization process involves both Fe oxidation and loss of K with a concomitant increase in the Mg content.

Halloysite with tubular morphology is formed in a wide range of geological environments from the alteration of various rock types. Intrusive acidic coarse-grained rocks, such as granites, pegmatites and anorthosite, with large potash and sodic feldspars contents, are subsequently altered to kaolinite, halloysite and other clay minerals by weathering or shallow hydrothermal fluid activity. Processing to separate the halloysite-kaolinite fraction from the altered host rock provides a product which can be used as a paper filler and in ceramics and fibreglass, among other uses, with various deposits in Brazil, China, Thailand and elsewhere. In the Kerikeri-Matauri Bay district of Northland, North Island, New Zealand, volcanic alkali rhyolite was extruded as domes and cooled rapidly with fine-grained feldspar subsequently altered to halloysite. The IMERYS plant in Matauri Bay separates the clay from the quartz-cristobalite matrix with an ∼20% yield of halloysite. The principal market is for high-quality porcelain and bone china that require low levels of Fe2O3 and TiO2. Deposits with high levels of halloysite occur in China, Turkey and the USA. The Dragon mine in Utah, USAwas recently reopened by Applied Minerals Inc. and now produces halloysite from zones of up to 100% white halloysite. Smaller occurrences of tubular halloysite are mined in China, Turkey and elsewhere from masses of comparatively pure clay that appear to have crystallized directly from solutions in which Al and Si were soluble.

The new mineral, dyrnaesite-(La), is found in the Ilímaussaq alkaline complex, South Greenland. The holotype material originates from an arfvedsonite lujavrite sheet as an accessory mineral. Dyrnaesite-(La) is pale yellowish green, with no cleavage and an irregular fracture. Density is 3.68(2)/3.682 g/cm3 (measured/ calculated). It is biaxial, negative, 2Vα = 47(1)/48 (measured/calculated); α = 1.6226(5), β = 1.6852(10), γ = 1.6982(2); X = c, Y = a, Z = b. The average values of microprobe analyses are (wt.%) P2O5 37.17, SiO2 0.15, CaO 0.90, Na2O 20.06, La2O3 16.44, CeO2 20.23, Pr2O3 1.40, Nd2O3 3.47, Sm2O3 0.24, Dy2O3 0.06, Y2O3 0.06.

The crystal structure was solved from single-crystal X-ray diffraction data. Dyrnaesite-(La) is orthorhombic, Pnma; a = 18.4662(7) Å, b = 16.0106(5) Å, c = 7.0274(2) Å, V = 2077.7(2) Å3, Z = 4. The structural formula calculated from the diffraction data and microprobe analysis is Na7.89(Ce0.94Ca0.06)∑1.00(Ca0.12La1.14Ce0.40Pr0.10Nd0.24)∑2.00(PO4)6, the simplified formula is Na8Ce4+REE2(PO4)6. The crystal structure is related closely to that of vitusite-(Ce), but is distinct from it in several aspects. The five strongest lines of the powder X-ray diffraction pattern are (d Å, (I %), (hkl)); 6.57 (100) (101), 4.62 (40) (301, 230, 400), 3.50 (40) (331), 2.80 (86) (232, 402), 2.67 (54) (060,630).

Rice bran constitutes about 10% of brown rice and is used as an animal feed. There are 40–45 million tonnes of rice bran produced annually, mainly in the Far East and South-east Asia. In these areas hull adulteration can occur, reducing the quality of the bran. This can now be detected by a simple colormetric method. Rancidity is a major problem due to the high oil content of the bran. Rapid hydrolysis of the oil is followed by oxidation with the changes being accelerated in warm, humid conditions. The effects on nutritive value and acceptability are unclear. An analysis of Australian produced rice bran (on a dry matter basis) gives a mean crude protein concentration of 150 g/kg, ether extract of 220 g/kg and neutral detergent fibre of 220 g/kg. The amino acid profile is generally superior to that of cereal grains. Digestibility of the oil is much less in young chickens than in adult birds resulting in a 28–35% lower metabolizable energy (ME) depending on cultivar. Equations for predicting the ME of rice bran for birds at different ages, and chemical components from rice hull content of rice bran are given. Digestibility of amino acids in rice bran is also lower for young chickens than adult birds. Inclusion of rice bran in chicken diets in excess of 20% frequently depresses growth, but higher levels can be tolerated by ducklings. Results with ducklings suggest that the composition of the basal diet to some extent influences the response of birds when rice bran is included in the diet. The inclusion of animal protein elicits an improved performance compared with that of an all-vegetable based diet. Defatted rice bran (DFRB) gives the same performance as full fat bran when equalized for ME. Laying birds can tolerate high levels of rice bran. Although some reports indicate successful inclusion of well above 600 g/kg, a practical upper limit of 450 g/kg seems to be accepted. Defatted rice bran at 250 g/kg diet resulted in leg problems, increased mortality and reduced egg output. Shell grit alleviated the problem. So far, attempts to improve the nutritive value of rice bran through addition of feed enzymes have had limited success. Feed phytase has been successful in releasing phosphorus from phytate in rice bran which is present at up to 50 g/kg dry matter. Improving the nutritional value of rice bran by heat treatment is probably not economical, although extrusion cooking will stabilize the oil before extraction and is used to stabilize rice bran for human food. Feed enzymes may be effective when a suitable combination is found.