Dadsonite was previously described without a name: (mineral Q) from Yellowknife, N.W.T.; (mineral QM) from Madoc, Ontario, and Pershing County, Nevada. Material from a fourth locality (Wolfsberg, Germany) yields good powder patterns, identical with those of QM, and single crystal data identical with those for Q.

Microprobe analysis of the Nevada and Wolfsberg samples gave, respectively, Pb 49·3, 50·8; Sb 31·7, 31·8; S 20·7, 20·3; sum 101·7, 102·9 %, giving Pb11Sb12·0S29·8 and Pb11Sb11·7S28·4, ideally Pb11Sb12S29 or 11PbS·6Sb2S3. Dadsonite is acicular [010], monoclinic, space group P2, Pm, or P2/m, with a 19·05, b 4·11, c 17·33 Å, β 96° 20′, Z = 1, Sp. gr. 5·76. The strongest lines of the X-ray pattern are 3·78 (7), 3·62 (6), 3·38 (10), 2·84 (7), and 2·79 Å (6).

Three of the members of the plagionite group, fülöppite Pb3S8S15, plagionite Pb5Sb8S17, and semseyite Pb9Sb8S21, show linear correlations of cell volume and density versus PbS:Sb2S3 mol ratios. This relationship can be used better to define the nature of the fourth member of the group, heteromorphite, Pb7Sb8S19. The cell dimensions derived for heteromorphite are a 13·60, b 11·93, c 21·22 Å, β 90° 50′.

Staringite, (Fe,Mn)0·5(Sn,Ti)4·5(Ta,Nb)1·0O12, occurs as inclusions in tapiolite from pegmatites at Seridózinho and Pedra Lavreda, Paraiba State, NE. Brazil. An indexed powder pattern is presented. The mineral is tetragonal with a 4·742 Å and c 9·535 Å, and most probably has a ‘trirutile’ structure. Electron-microprobe analysis yielded Ta2O5 21·5%, Nb2O5 1·8, SnO2 73·3, TiO2 0·03, FeO 3·7, MnO 0·3, sum 100·6%. Dcalc 7·17. Micro-indentation hardness (load 100 g) 1033–1187 kg/mm2; reflectivity at 470 nm (R0) 12·8 to (R′e) 14·5%, at 546 nm 12·1–13·9, at 589 nm 12·0–13·7, and at 650 nm 11·8–13·6; staringite is uniaxial positive.

Harmotome, associated with analcime, is described from andesite dykes at Rehia and Maungarahu in the Tokatoka district, New Zealand. The Maungarahu harmotome has the composition: (Na1·03K0·23)(Ba1·54Ca0·18)Al4·66Si11·31 12·39 H2O; physical properties: α 1·498, β 1·503, γ 1·506, 2Vγ 75–82° β:[001] 28° D 2·378; and cell constants: a 9· 906±0·006, b 14·119 ±0·003, c 8·712±0·007 Å, β 124° 57′ ± 3′. The harmotome is Ba-poor, and 2 Na+ has substituted for Ba2+ on a valency basis. Analcime associated with the Maungarahu harmotome has chemical composition: (Na15·16 K0·03Ca0·09)Al15·52Si32·47 15·93 H2O and physical properties: n = 1·483, D = 2·257, a = 13·708 Å. The zeolites are believed to have crystallized from Na and Ba-rich alkaline solutions at approximately 200°C The source of the Ba is baryte concretions in adjacent limestones.

The system sanbornite-celsian has been investigated by the quenching method, and the results compared with earlier studies. The system is essentially a simple binary eutectic system with little or no solid solution. The eutectic is located at a composition of 69% sanbornite and 31% celsian (by weight) and at a temperature of 1227±3°C. No evidence for substantial solid solution of celsian in sanbornite, as reported in previous work, was found. Paracelsian, a naturally occurring polymorph of celsian, was not encountered in the study.

Cordierite commonly alters to chlorite-sericite, called pinite. Besides pinite alteration, cordierite from the Fishtail Lake shows textural evidence indicating retrogression to kyanite, andalusite, and coarse flakes of chlorite. This is consistent with the experimental data on the stability of cordierite and may be expected to be limited to potash-deficient rocks, such as the cordierite-garnetgedrite bearing gneisses of the area. In common potash-bearing pelitic rocks, retrogression of cordierite results in the formation of sericite and chlorite. In gneisses containing sillimanite and cordierite, the breakdown of cordierite in this way results in the association of the three aluminosilicates (kyanite, andalusite, and sillimanite) in the same rock. The association of kyanite-andalusite in equilibrium probably suggests that the retrogression of cordierite took place close to the univariant line of kyanite-andalusite.

A study of augite in over three hundred thin sections of mainly alkalic rocks permits the distinction of two main types of hour-glass structure. The common ‘swallow-tailed’, sometimes skeletal augite crystals are found in the fine-grained groundmass of many rock types, and it is suggested that rapid crystallization alone accounts for their formation. Hence, this type of hour-glass structure has been called ‘quench hour-glass’. The hour-glass structures of larger augite crystals of porphyritic and coarse-grained rocks are commonly described as hour-glass ‘zoning’, as they result primarily from compositional differences between the different sectors. These were formed under conditions of relatively slower cooling than the ‘quench hour-glass’, and thus cannot be explained in the same way. They are thought to have formed by a process involving adsorption of impurities on a particular crystal face so as to impede growth of these faces, producing an initial skeleton of hour-glass form, which is completed by later crystallization of augite richer in FeO, Na2O, TiO2, and Al2O3. This hypothesis also explains the patchy zoning of other augite crystals, casting doubt on some petrogenetic interpretations of such zones as core zones.

Clinoptilolite-heulandite is reported from Jurassic, Cretaceous, and Palaeocene sediments in south-east England. It occurs mainly in 1–20 μm size fractions, and is associated with abundant montmorillonite and often also with glauconite and amorphous silica or low-temperature disordered cristobalite-tridymite. Its mode of occurrence and the associated minerals suggest an authigenic origin, but there is no evidence that the source material was volcanic.

Forty-three natural alkali feldspars have been homogenized and used to correlate with wt % K2O. The regression of Or on is Or (wt %) = 465·5 (Å)-1877·5, and is comparable to that obtained on an exchanged orthoclase (Wright, 1968). A deviation from the Orville (1963, 1967) determinative line for synthetic sanidine-albite is greatest at the high potassium end of the series. The discrepancy is not caused by failure to homogenize or incomplete disorder. The presence of cations other than potassium and sodium, or cation deficiency, or both cannot be discounted as a cause.

An unusual occurrence of porphyritic plagioclase-hornblende-pyroxene granulite (porphyritic basic charnockite) has been observed within the ‘Charnockite region’ of the Eastern Ghats of the Precambrian formations of India. From the X-ray and chemical data the phenocrysts are considered to be augite phenocrysts. Based on petrographic and chemical evidence it is inferred that the basic charnockites of Chipurupalli area in Visakhapatnam district are formed from tholeiitic magma as a gabbroic mass under deep seated plutonic conditions. The gabbroic mass has been recrystallized as plagioclase-hornblende-pyroxene granulite due to later metamorphism, leaving most of the phenocrysts unaffected.

A group of ultrabasic dykes occurring in south-west Skye is typified by often abundant and diverse ultrabasic xenoliths composed of essentially the same minerals as the dykes. The xenoliths, which vary considerably in shape and size, are in sharp contact with the host rocks and exhibit no evidence of remelting by, or reaction with, the dykes. Although extensive axial concentration of olivine occurred in the dykes during intrusion, the xenoliths appear to be randomly distributed throughout all but the extreme margins of the dykes and often exhibit a preferred orientation. The orientation and distribution of the xenoliths are attributed to the suppression of rotation and axial migration of the xenoliths during the emplacement of the dykes because of the relatively high viscosity of the suspending medium.

The ultrabasic xenoliths, unlike many of those occurring in basalts, kimberlites, etc., are considered unlikely to represent primary upper mantle material and it is suggested that they were probably derived by the disintegration of layered ultrabasic rocks genetically related to the dykes and hence are of cognate origin.