At least five successive intrusions of nepheline-bearing magmas fractionated in situ and developed repeatedly overlapping, yet distinct chemical trends in the mafic silicates. Representative electron probe analyses are given for olivine, clinopyroxene, amphibole, biotite, and aenigmatite and their variations discussed. Increasing Na with fractionation produced aegirine-rich clinopyroxene and caused Na/K in amphibole to increase from 2.4 to 7.0. Siz/Alz increased in both amphibole and in the less abundant mica. Mn-enrichment is common to all of the mafic silicates, including the olivines and it is suggested that the parent magmas were initially Mn-rich.

Mineralogically the Motzfeldt centre is evolved and similar to the other centres in the Igaliko complex. However, the Motzfeldt centre contains the most fractionated rocks (lujavrites) and is in this respect similar to the peralkaline Ilimaussaq intrusion. The compositional ranges and trends of the mafic silicates in Motzfeldt thus provide links between the uncommon peralkaline plutons and the more abundant and typical nepheline syenites.

Alkaline mafic sills of Jurassic to Cretaceous age in the Oman Mountains have coarse-grained wehrlite centres composed of olivine and zoned diopside-titanaugite with large interstitial poikilitic titanian hornblendes and titanian barian phlogopites and biotites which appear to have crystallized from a trapped, intergranular, volatile-rich liquid. The fine-grained chilled margins of the sills are olivine-poor and composed largely of titanaugite, kaersutite, sphene, and interstitial altered plagioclase. The rocks have high contents of incompatible elements (Ti, P, Sr, Ba, Zr, Nb, and others) and steeply inclined, light element enriched, REE patterns. The parent magma is estimated to have been a hydrous alkali picrite with c. 12% MgO from which the wehrlite formed by olivine accumulation. The unusual tectonic setting of the sills, in a Mesozoic continental margin sequence emplaced in an Alpine thrust belt, is noted.

Garnet porphyroblasts in metasediments from Magerøy crystallized during static metamorphism. They display three optical zones, each having characteristic inclusions and chemistry. The compositional zoning is related to prograde metamorphism (an inner zone, 1, and a graphite-bearing zone) and retrogression (the outer zone, 2). Inclusions of two types are present in zone 1: type 1 are equidimensional remnants of the matrix, preferentially included along planes of rapid growth; type 2 are tubular and represent recrystallized quartz grains concentrated along defects in the garnet lattice. The defects are lineage boundaries between growth segments related to screw dislocations on crystal faces. Crystal growth developed at relatively high degrees of supersaturation, but below the supersaturation required for the development of dendrites. The inclusions suggest rapid growth of zone 1, caused by heat flow from an adjacent interkinematic mafic/ultramafic intrusive complex. The graphite-bearing zone crystallized at the metamorphic peak, while the inclusion-free idioblasfic rim probably developed during retrograde metamorphism.

Malayaite and tin-bearing garnet occur within a skarn assemblage at Gumble, NSW. A metasomatic origin is proposed for these minerals under conditions of T = 300-500°C Xco2 < 0.30 and fO2 = 10−18 to 10−30 bars. Malayaite has formed as a result of reaction between a metasomatic fluid rich in Sn, F, H2O and silica, and tin-bearing andradite and wollastonite. The main requirements for tin-bearing skarn formation appear to be an F-Sn-rich granite, an iron-rich skarn assemblage, and a relatively long cooling history.

Uvarovite and grossular, the former comparatively rare, occur along the serpentinite-graphite schist contact in the Fengtien area, on the eastern slope of the Central Range of Taiwan. Uvarovite occurs as small emerald-green euhedral crystals on diopside-fels with dodecahedral crystal forms and many other modifications. Its refractive index is 1.782, specific gravity 3.702, and unit cell edge 11.912 Å. Chemical and probe analyses give average Cr2O3 contents of 11.60 wt. %; spectrographic analysis shows significant enrichment in Cr, Be, Co, Y, Sb, and La over grossular. Associated minerals include nephrite, diopside, tremolite asbestos, zoisite, and clinozoisite. Grossular is reddish-brown; large crystals, dodecahedral in form often modified by trapezohedrons, are associated with diopside, idocrase, and calcite. n = 1.746, SG = 3.636, and a = 11.866 Å. Structurally and chemically it is quite near the grossular end member. Grossular is considered to be formed from pneumatolysis associated with the intrusion of ultramafic rocks, whereas uvarovite is a replacement product of relict chromite in the original ultramafic rocks where migration of elements such as silicon and calcium from wall rocks are prominent.

Ca- and Na-rich pyroxene compositions of four agpaitic phonolites from the Cantal Volcano (France) have been studied. The pyroxenes from each sample show a range of compositions between X2+ pyroxencs (with X = Ca, Mg, Fe2+) and aegirine. The main substitution, X2+ by (Fe3+ + Na+), occurs when Na-Mg = 0.5, by which time Si is already equal to 2.0. The crystallization of Fe-Na-rich pyroxenes seems to be related to the increasing peralkalinity of the environment, in which the initially high temperature was suddenly reduced. Other factors, such as the structure of the liquid, are also considered.

Sub-greenschist facies metamorphism has produced unusual subcalcic, Fe-rich actinolitic amphiboles in meta-dolerites from the Glenrock Station area, NSW. They show edenite, riebeckite, ferri-tschermakite and Ti-tschermakite coupled substitutions. Their high Fe content is attributed to high aFe2+ and aFe3+ in the fluid phase produced during the breakdown of clinopyroxene, hornblende, magnetite, and ilmenite. The high aFe2+ led to Fe led to Fe2- occupying the B site, resulting in the formation of subcalcic amphiboles. Variation in aFe2+, aFe3+, aMg, aSi, aAl, and aCa, in different domains resulted in the crystallization of chemically inhomogeneous amphiboles.

Most of 325 K-feldspars from the Hida metamorphic belt are characterized by diffuse 131 and 11 reflections. These K-feldspars are classified into eight obliquity types on the basis of the width of the 131 peak or the ratio of mean height of two outer peaks (131 and 11) to that of the middle composite peak. From the distribution of obliquity types and the microscopic characteristics of K-feldspars, this area is divisible into six zones.

The feature of each zone is shown by the frequency distribution of eight obliquity types in each zone, which reflects the strength of later retrogressive effects. The frequency distribution of Δ values in each of the types IV-VIII provides further information on later events.

The result of the K-feldspar study possibly indicates that the inversion of monoclinic to triclinic K-feldspar, characterized by the development of perthitic texture or crosshatched twinning, is sensitive to the degree of later retrogressive events. Some data on 2θ values of 04, 060 and 01 reflections in each types are presented.

Tetrahedral framework compounds, as defined in this paper, generally exist as tilted and distorted versions of ideal fully expanded structures at room temperature and atmospheric pressure. How pressure, temperature, and composition (P, T, and X) affect the tilting and distortion is critically reviewed. It is shown that although the effects of P, T, and X on the cell parameters are broadly analogous, the underlying structural changes are generally different. An important, and frequently neglected thermal effect is the apparent shortening of the framework bonds by the anisotropic thermal motion of the framework oxygens. Tilting models of framework compounds are critically examined and their failure to match the observed structural behaviour is attributed to changes in tetrahedral distortion. For quartz it appears that during compression the change in tetrahedral distortion is virtually all angular (O-Si-O angles), whereas during thermal expansion the change in distortion is in the Si-O distances. Such behaviour may typify the behaviour of many other framework compounds but the structural data needed to establish this are lacking. The review is illustrated by reference to the quartz and cristobalite analogues; to the sodalite, leucite, nepheline, scapolite, and feldspar families; and to the nitrides and oxynitrides of silicon and germanium. It is concluded that our understanding of the structural behaviour of framework compounds is still superficial and that much theoretical and experimental work remains to be done.

Phlogopite mica has crystallized from blast-furnace slags at atmospheric pressure. Its chemistry is characterized by an excess of Na and K over their normal stoichiometric content, which is attributed to a composite association between phlogopite and glass. The diffraction pattern indicates that the phlogopite has a preferred orientation around the a-axis. Scanning electron microscopy shows that this phlogopite consists of numerous small platelets, which probably have their a-axes aligned.

Copper mineralization at Tomnadashan is associated with granitic lenses intruded into a small Caledonian diorite body. The mineralization occurs as disseminations and irregular veinlets and mainly comprises pyrite, chalcopyrite, tetrahedrite-tennantite, calcite, and quartz. There are small inclusions of bismuthinite, galena, aikinite [(Cu,Pb,Fe,Bi)S3], and a mineral with a chemistry similar to hodrushite (Cu8Bi12S22). The tetrahedrite contains up to 6.1 wt. % bismuth.

Four km to the south, at Corrie Buie, are quartz veins, hosted by meta-limestones, containing galena with minor amounts of chalcopyrite, pyrrhotite, sphalerite, electrum, schirmerite, and lillianite homologues.

The mineralogy of both deposits is consistent with that associated with acid magmatism. There are mineralogical similarities between the two deposits but the style of mineralization at Tomnadashan suggests a limited hydrothermal system and therefore the Corrie Buie veins may be related to felsic intrusives to the south.

Eggletonite is a new mineral, the Na analogue of ganophyllite. Type material has composition

(Na0.82K0.40Ca0.39□0.39)Σ2.00 (Mn6.61Zn0.08Mg0.16Fe0.61Al0.56)Σ8.02 (Si10.33Al1.67)Σ12.00[(O28.92(OH)3.08]Σ32.00 (OH)4.00·10.66H2O.

It occurs as prismatic crystals elongated along [100] in miarolitic cavities in nepheline syenite at the Big Rock Quarry, Little Rock, Arkansas. Single-crystal X-ray diffraction data are consistent with space group I2/a or Ia; a = 5.554, b = 13.72, c = 25.00Å, β = 93.95° Z = 2; this is equivalent to the substructure of ganophyllite. Physical properties include cleavage: {001} perfect; colour: dark brown; translucent; streak: light brown; hardness (Mohs): 3–4; brittle; observed density 2.76, calculated density 2.76 g/cm3. Optically, eggletonite is biaxial negative, with optical parameters 2Vα = 9(3)° r < ν, weak; indices of refraction α = 1.566(2), β = 1.606(2), γ = 1.606(2); pleochroism is very weak, γ ≃ β > α; α = pale brown to colourless, β ≃ γ = pale yellow brown. Principal lines in the X-ray powder diffraction pattern are (d, I/Io): 12.4, 100; 3.45, 15; 3.13, 30; 2.854, 15; 2.691, 25; 2.600, 20; 2.462, 20; 2.387, 15. The name is in honour of Dr Richard A. Eggleton, Australian National University.

A Zn- and Y-group-bearing senaite, formulated as AM21O38 (Pb0.63Na0.46Ba0.11)Σ1.20(Ti14.64Zn1.74Y‒group REE0.70Mn0.38Nb0.20Sn0.03Zr0.03Th0.02)Σ20.9O38, a member of the crichtonite group, is a newly characterized phase associated with murataite at the St Peters Dome area, Colorado. The Zn- and Y-group-bearing senaite is uranium-free and nonmetamict, but otherwise is comparable to known senaites and davidites in X-ray diffraction pattern, symmetry, and structure. The REE distribution shows a strong dominance of Y and the Y-group REE which are present in M(1). Megascopically, the mineral is black, submetallic, and opaque; in polished section it appears to be white and moderately bright compared with murataite. Cleavage is absent but twinning on {520} is present.

Senaite and hitherto unreported zinc-bearing senaite from Dattas, Diamantina, Minas Gerais, Brazil, have the following respective structural formulas as determined by electron microprobe:

(Pb0.76Sr0.20La0.08Ce0.07Ba0.04)Σ1.15(Ti12.89Mn0.88Y0.59Zn0.12Mg0.07Nb0.03Cr0.02Th0.02)Σ20.61O38

and

(Pb0.89Ba0.15Ce0.02Sr0.02)Σ1.08(Ti14.57Zn1.76Na0.63Mn0.50Y0.28Nb0.14Mg0.04Cr0.02)Σ20.83O38

The historical background leading to the discovery of sarcolite by Thomson is reviewed. Many mineralogical reference works quote Thompson (1807) but no paper on sarcolite by Thomson has been found; also the spelling of Thomson is incorrect on numerous occasions. The history of sarcolite from its original discovery is reviewed. Chemically, sarcolite is inadequately characterized in spite of a structural study by Giuseppetti et al. (1977). All known chemical analyses are collated and discussed. Two new analyses, using a combination of gravimetric, colorimetric, atomic absorption, and electron probe methods, are presented which show sarcolite to contain 2 wt. % flourine. The presence of this element in sarcolite was reported in 1860 but no quantitative data given; the new determinations cast some doubt over certain aspects of the sarcolite structure.

Measured densities of sarcolite range from 2.93 to 2.96 (mean 2.95) gm/cm3; the tetragonal unit cell of a 12.32 and c 15.48 Å leads to a calculated density of 2.925 gm/cm3 using the empirical formula. Empirically sarcolite may be expressed as:

Na1.38Ca6.0(Ca0.37,K0.13,Fe0.08,Sr0.07,Mg0.05)Σ0.70 Al3.90Si6.02P0.54O26.20F1.06C0.06

and ideally

Na2Ca12(Ca,K,Fe,Sr,Mg)2Al8Si12(P,Si)O52F2

and suggests 27 (oxygen and fluorine) atoms in the quarter unit cell.

Details are given of the mineralogical assemblage, optical properties, infra-red and thermal behaviour of sarcolite which, after 176 years, is still known from only one locality—Monte Somma.

An occurrence of a celadonite-like mineral in a weathered basalt in the Lake District has been investigated by X-ray diffraction, X-ray fluorescence, electron microprobe, and infra-red spectroscopic methods. The bulk composition of the mineral corresponds to an aluminous-glauconite. The data show that the mineral is most probably a celadonite-muscovite or celadonite-illite mixture, although a celadonite-phengite cannot be entirely discounted. Approximately 10% smectite layers are also present. The results suggest that re-examination of many aluminous glauconites may show them to be mixtures of this type.

Variation in composition, Fe3+/Fe2+ ratio, per cent mixed-layering, and d(060) spacing have been determined both between and within grains of glauconite from the Folkestone Beds at 286.5 m in the Tollgate bore, Sandwich, Kent. Grains extracted from the rock were classified on the basis of size into large (> 1 mm) and small (< 1 mm), and on colour into light and dark green. Large grains have a progressive increase in Fe3+/Fe2+ ratio with increase in total iron, while small grains have variable ratios; the largest variation is in the dark grains. The effect of the range of Fe3+/Fe2+ ratio variations on structural formula (e.g. R3+) is discussed. The per cent mixed-layering is not related to colour. There is a greater variation in Al, Fe, and K contents in and between large grains than small grains. Both sizes of grains may be separated on d(060) spacings determined by X-ray diffraction. Glauconite from coral and gastropod casts has different d(060) spacings than that from bryozoan casts and variegated grains, but is similar to the small grains. Large light grains may have developed from small light grains but it is unlikely that the large dark grains developed from small dark grains. The large grains probably all formed under similar conditions, with a common origin; the small from several sources or from a single source under a variety of conditions.

Macaulayite was found by the late I. Stephen (Soil Science Department, University of Aberdeen) in an outcrop of reddened, deeply weathered granite, near Inverurie, Aberdeenshire. It is blood red in colour, very fine-grained, and has refractive indices greater than 1.734. Its calculated density is 4.41 g/cm3. The mean of fourteen electron microprobe analyses in the anhydrous form is Fe2O3 84.67, Al2O3 4.01, SiO2 11.32%. With thermogravimetric data this leads to a formula of (Al3.38)Si7.95O86(OH)4; the ideal formula is Si4O43(OH)2. The cell indexes as C-centred monoclinic with a 5.038, b 8.726, c 36.342Å, β 92°. The strongest X-ray lines are 36.6 (vs), 18.16 (vs), 3.700 (25), 2.720 (35), 2.533 (100), 2.214 (20), and 1.420 (35). Macaulayite has a layer structure, thought to consist of a double hematite unit terminated on both sides by silicate sheets and with water between these sheets. The infra-red spectrum includes absorption bands at 3597, 1052, 1033, and 858 cm−1, arising from the hydroxysilicate component of the mineral and at 647, 520, 438, 400, 304, and 227 cm−1 corresponding to the platy hematite unit. The mineral is named for the Macaulay Institute for Soil Research and the name was approved by the Commission on New Minerals and Mineral Names of the International Mineralogical Association prior to publication.

A new occurrence of zaherite is reported from a sillimanite quarry 65 km west of Pofadder, Bushmanland, South Africa. It occurs as earthy white to light bluish-green cryptocrystalline material in narrow veins, in close association with natro-alunite and hotsonite, a new hydrated aluminium phosphate-sulphate. Scanning electron micrographs show an orientated wavy texture and tubular fibres. The optical and physical properties agree with those of the type material described from Pakistan, and it can be added that the mineral is biaxial positive with a moderate 2V and length-fast orientation. The new chemical analysis yields an ideal formula of Al12(SO4)5(OH)26·20H2O, which is identical to that of the type material. The white and light bluishgreen varieties are identical in major element composition but yielded trace Cu values of 1281 and 2408 ppm respectively. The X-ray powder diffraction pattern fits a triclinic symmetry (a 5.55, b 9.74, c 18.43Å, α 99.71°, β 89.13° γ 94.97°), and is dominated by one intense reflection at 18.12 Å, representing 001. The most important of the weak lines are (d, I, hkl): 9.56, 5, 010; 9.08, 4, 002; 4.82, 6, 01; 4.61, 8, 110; 4.56, 4, 02; 4.44, 4, 021; 3.61, 4, 1; 3.22, 8, 015. The differential thermal properties are characterized by endothermic peaks at 190, 470, and 685°C and a duplex at 880 and 910°C The infrared absorption spectrum is characterized by absorption bands centring about 905, 960, 985, 1150, 1700, and 3600 cm−1.