Quetzalcoatlite is a new mineral from the Bambollita mine in the Sierra La Huerta near Moctezuma, Sonora, Mexico. The colour is Capri blue (R.H.S. 120A) with a pale streak. H = 3; G meas. = 6·05±0·3 G calc. = 6·12. Crystals up to 0·4 mm long were not measurable but are acicular to prismatic, hexagonal, with fair cleavage on {100}; a 10·097 Å, c 4·944, space group C632. Z = I. Strongest lines are 8·752 (100), 2·748 (70), 2·520 (42B), 3·531 (40), 3·273 (31), 1·766 (28), 5·054 (21), 2·250 (20). Electron probe analysis gives: CuO 20·3%, 18·9, 20·9; ZnO 41·2, 38·2, 38·7; TeO2 29·4, 31·3, 30·6. Water by Penfield method on 2.265 mg gave 10·1%. Empirical cell contents are Cu4·01Zn7·73Te3·04O8·88(OH)17·89 or Cu4Zn8(TeO3)3OH18. Pleochroic with ε = colourless, ω = pale blue-green; uniaxial (-) with εD = 1·740, ωD = 1·802. Named for the Toltec god Quetzalcoatl.

The crystal structure of buttgenbachite from Likasi (Congo) was solved by a three- dimensional Patterson function, computed using intensity data collected photographically by the Weissenberg method, and refined by successive Fourier maps and least-squares refinement to an R index 0·055 for 328 independent observed reflections. The cell content resulting from the structural analysis is Cu36·6Cl6·7(NO3)2·6(OH)63·9.2·1 H2O. The space group is P63/mmc with a = 15·750 Å and c = 9·161Å. The buttgenbachite structure is not completely ordered. It consists of a rigid three-dimensional skeleton formed by Cu co-ordination polyhedra sharing edges and corners. The large channels in the framework show a zeolite-like nature; inside the channels the disorder is caused by the different orientations of nitrate groups and by the occurrence of the substitution . The crystal structure of buttgenbachite is closely related to that of connellite. The mechanism of forming an isomorphous series is discussed: the present study shows that the replacement is more complicated than was supposed in the literature.

The structure of julgoldite, , has been determined and refined to an R value of 4·6 % based on 2417 symmetry-independent reflections, of which 765 are unobserved (weighted R = 4·3 %). The cell dimensions are a 8·922(4), b 6·081(3), c 19·432(9) Å, β 97·60(6)°, the space group is A2/m with Z = 4 and Dcalc 3·56 g cm-3. Julgoldite is isostructural with pumpellyite; the Si-O and Ca-O distances of julgoldite are identical, within experimental accuracy, with corresponding distances in pumpellyite; the Fe-O distances of julgoldite are about 0·09 Å longer than the corresponding (Al, Mg)-O distances in pumpellyite. The four hydroxyl groups and the extent of O-for-OH substitution are identified by valence-sum calculations.

Comparison of the infrared spectra (4000-50 cm−1) of natural and synthetic samples of margarite, beryllian margaritc, ephesite, and clintonite indicates that the tetrahedral layers of margarite and ephcsite, containing Si and Al in equal atomic proportions, are ordered as the spectra are sharp and show no Al-O-Al vibrations. Clintonite of this tctrahedral composition is disordered. The hydroxyl-stretching frequencies are affected by ionic substitutions in both the octahedral and tetrahedral layers. The spectra permit the distinction of the different species of brittle mica. They also indicate the presence of beryllium in margarite, and allow an estimate of the tetrahedral composition of clintonites.

Chemical analyses of sixteen lithium-aluminium micas are presented along with their optical, physical, and X-ray data. Compositional variation, substitution relations in structural positions, and octahedral occupancy are discussed. The 2M2 structural types are found to crystallize in volatilerich low-temperature environments whereas the 1M polytypes occur in comparatively volatile-poor and higher-temperature environments. Variation diagrams have been constructed to show the relationship between octahedral sites occupied by and refractive indices and specific gravities.

Twenty-six compositions in the system MgO-Al2O3-SiO2-H2O were investigated under conditions of 1 and 2 Kb water pressure and temperatures between 300 and 700°C. The solid solution for 7 Å and 14 Å chlorites has been delimited as well as that of the expanding phases (tri- and dioctahedral montmorillonites and expanding chlorites). Negative slopes were found for the transformation montmorillonite → expanding chlorite, and expanding chlorite → chlorite+quartz and a positive slope for 7Å → 4 Å transformation. The relative positions of the reactions chlorite+quartz → cordierite+talc, chlorite+andalusite → cordierite and chlorite+corundum → cordierite+spinel are located between 500 and 65°C.

Cell dimensions of the synthetic chlorites can be correlated with their chemical composition. Solid solution in synthetic minerals compares well with 325 analysis of natural minerals from the literature, indicating that the chemiographic relations between phases in the simplified synthetic system are applicable to natural mineral assemblages. The phase relations indicate that at low temperature the 7Å aluminous chlorite is not stable with quartz or another silica phase.

Clinopyroxene crystals with complex lamellar intergrowths of orthopyroxene and garnet are described. The orthopyroxene lamellae are irrationally orientated within the clinopyroxene host although the optical relationships of these minerals are consistent with (100) exsolution in clinopyroxene. The intergrowth is nevertheless considered to be the result of exsolution processes. Possible modes of origin are reviewed together with the general significance of exsolved pyroxenes in eclogite- and granulite-facies associations.

The observations of hour-glass sector zoning from four selected clinopyroxenes in undersaturated lavas best fit a model in which the sector zoning is formed due to a structural requirement in a growth direction normal to {100} where a high concentration of silicate units, required to build the silicate chains, is unsatisfied. In these sectors Al substitutes for Si, the charge balance being maintained by octahedral substitutions, of which Ti contributes to the deeper colour of the sectors. The presence of concentric zoning only reflects a change in temperature and a change in the composition of the liquid during crystallization of the pyroxene.

Approximately forty, variously shaped, chromitite bodies occur in dunites and harzburgites of the alpine-type peridotite complex of southern New Caledonia. The chromitites consist of pichrochromite (59 to 42% Cr2O3) and serpentinized olivine (Fo96-92) and display a variety of textures (massive, disseminated, and orbicular) consistent with a magmatic cumulate origin. Dunites contain olivine (Fo93−97) and 1 to 3% picrochromite (50 to 39% Cr2O3). Harzburgites have less than 1% spinel, ranging from picrochromite to ceylonite (45 to 28% Cr2O3) and often forming symplectic intergrowths with bronzite. Temperatures of crystallization of the cumulate picrochromites are believed to have been about 1200 °C while the more aluminous symplectic spinels equilibrated under different conditions and may reflect a late stage recrystallization episode.

At least four stones fell over a distance of about 9 km at the end of a west to east trajectory on 25 April 1971 at about 1630 hours local time. Their approximate location is 11° 51′ N., 8° 13′ E. About 13·4 kg of this xenolithic bronzite chondrite, class H4, were recovered. A bulk chemical analysis with total Fe = 29°4 % (wt), is presented. Olivine is Fa18.9 (molec.) in composition. Concentrations of the cosmogenic radionuclides 22Na, 26Al, and 54Mn were 71±6, 56±5 and 84±6 dpm/kg, respectively.

Urea, a new mineral identical with the artificial compound, occurs as crystals associated with phosphammite, ammonian aphthitalite, and weddellite in guano from Toppin Hill, 123° 56′ E., 28° 42′ S., Western Australia. The urea occurs as elongated tetragonal pyramids, space group , a 5·646, c 4·701 Å, X-ray powder data are given. Optical properties: ω 1·484, ε 1·603. Chemical analysis gave urea, CO(NH2)2 96·0, H2O− 0·46, Na 0.13, K 0·35, Ca 0·07, Mg 0·03, S 0·11, P 0·24, NH3 < 1·0 %, remainder probably mainly H2O+; urea 96 %, impurities 4 %. Type material is preserved in the collection of the Government Chemical Laboratories, Perth, Western Australia.

Heating experiments provide strong evidence that the transparent green coats on some diamonds from each of many localities are caused by α-particle irradiation after kimberlite injection and subsequent cooling. The natural diamonds with more or less homogeneous transparent green coats, studied in this work, appear to have received doses of at least 5 × 1013−1 × 1014 α.cm−2. For Pre-Cambrian kimberlites, such doses could occur if certain regions of the diatremes contained ⩾20 ppm by weight of equivalent uranium, after kimberlite injection and solidification.

Such considerations lead to the prediction that the radioelement concentrations in the Finsch kimberlite diatreme and the Bellsbank fissure kimberlite are considerably greater than those in the Premier mine, though radioelement segregation could produce the required local concentrations. Some exploratory autoradiographic measurements made on two kimberlite rock samples from Premier and De Beers Mines indicated that the radioelements were apparently distributed on a submicron scale, which would be a necessary, but not sufficient, condition for uniform α-irradiation of diamonds.

Diamonds from various alluvial sources showing green and brown spots arising from much heavier and more localized radiation damage are also discussed.