The crystalline form of orpiment was first determined by Mohs (Grundriss der Mineralogie (1824), 2, 613).

His measurements, which he is careful to state were only approximate, gave an angle of 79°20' for the prism, and 83°7' for the brachydome; the plane of perfect cleavage being taken as the macropinakoid, and the crystals being referred to the orthorhombic system.

During an optical examination of many mesolite crystals with a view to a determination of their symmetry, the author was puzzled to find that whereas mesolite has generally been described as anorthic, on optical evidence, he could detect no trace of inclined extinction in the prism zone. A. Cavinato (1926) 1 and G. Ceshro (1909) 3 had already made similar observations. Further study revealed the probable causes of the discrepancies, and as these sources of error, and the precautions necessary for their avoidance, receive little or no mention in the principal text-books, an account of them might be of some use.

Early in the year 1918 Mr. Atehur Russell picked up at the old antimony-lead mine at Glendilming in Eskdale, Dumfriesshire, Ipecimens of the antimony-lead ore Jound there, in which were small cavities lined with a drusy layer of mimlte crystals; these, being markedly deeper in eolour than the stibnite forming part of some of the specimens, belonged to a different species, and probably a sulphantimonite of lead. Mr. Russell blought some of the specimens to the Museum, and some of the small crystals were examined with the view of determining the species to which they belong.

This mineral, which until now has been regarded as a hydrated arsenate of iron, was mentioned as far back as 1790 by Proust and also by other mineralogists about the same time. In 1801 Chenevix (Phil. Trans. 1801, 220) gave an analysis of an arsenate of iron, but it differs very much in composition from pharmacosiderite in that it contained 9 per cent. of copper. Probably it was not a pure specimen of this mineral. Vauquelin also published an analysis of an iron arsenate which was probably pharmacosiderite (Brongniart, Traité de Min., 1807, II. 182), since he describes it as crystallising in cubes.

When investigating the morphology of crystals, such as those of schwartzembergite, which are so rounded or striated as to afford no definite reflections of the object-slit of the goniometer, the author found most serviceable a camera lucida which could be attached to the eye-piece of the telescope of the goniometer, and thus used for the direct drawing upon paper of the ‘light-figures’ given by the crystals, the ordinary signal being replaced by a pin-hole. The cap of the eye-piece in use is unscrewed and the camera lucida is fixed to the tube by means of four clamping screws.

Specimens of delorenzite from the type locality, Craveggia, Val Vigezzo, Piemont, have been examined and found to be close to tanteuxenite from Australia. The X-ray powder patterns are virtually the same, and the chemical analyses (including the relative abundances of the rare earths) are closely similar.

Zambonini's original (1908) specimens have not been re-examined, but are without reasonable doubt the same as the specimens now described; the considerable discrepancies between the old and new analyses can be explained by the difficulty of the separations. It is suggested that the name delorenzite be abandoned despite its priority because of its association with an incorrect analysis.

On Saturday, September 18, 1902, at 10.30 a.m. (Irish time), a stone coming from the sky struck the earth (let. 54° 88' 20" N., long. 6° 12' 10" W. of Greenwich) at a farm, belonging to Mr. Andrew Walker, situated in the district termed Crossbill, a mile to the north of the village of Crumlin, in which there is a station of the same name on the line of railway between Lisburn and Antrim. The place of fall is 3½ miles east of Lough Neagh, the largest lake in the British Isles, and I2 miles almost due west of Belfast, in which city nearly two thousand members of the British Association were then assembled for the annual meeting (September 10-17).

In working on the isomorphism of Tourmaline I have been struck by the very peculiar development of a fine crystal from Pierrepont, New York, now in the Cambridge Collection.

The crystal is doubly terminated, of a jet-black colour and splendid lustre. It weighs 814.88 grammes, and measures 1⅙ inch by 1 inch by ½ inch.

It is now well recognized that quartz undergoes a sudden change near 575° C., and Wright and Larsen (1) have shown that the characteristics of quartz formed above or below this point are so marked that they can be utilized to determine the temperature of formation of rocks containing quartz. Quartz formed above 575° so-called β-quartz, is of distinctly hexagonal development, and occurs generally as regular hexagonal bipyramids with or without a subordinate prism-face. These external characteristics are of course preserved on cooling, and the bipyramids are converted into apseudomorphous aggregate of α-quartz.

The separation and estimation of small quantities of manganese in the course of exact analysis of igneous and metamorphic rocks has long presented a difficulty. The element is almost universally present, in amounts varying from a few hundredths of one per cent. to over one per cent., the higher figure being reached in the basic rocks, especially in those rich in ferromagnesian minerals. In the ordinary course of analysis, if no special method be adopted to separate and remove manganese, this element tends to be distributed between the 'ammonia precipitate' and the lime and magnesia. It has been shown by G. Steiger that when the usual methods are employed, the manganese tends to be distributed in a quite haphazard way among the three precipitates; no definite proportion is retained by any one of them, although as a general rule most of the manganese is found with the magnesia and least with the lime.

Considerable interest attaches to the estimation of the volume occupied by the several atoms in a crystalline compound. For the complete molecule a volume can at once be calculated from the density and the chemical composition, but the further subdivision of this space into domains belonging to the constituent atoms or groups can only be made by methods that are limited and frequently very indirect. In general, the volume is not additive, and. it seems clear that the same atom may occupy very different volumes in its different compounds; indeed, it is only within the limits of a truly isomorphous series that the volume can be treated as an additive property. But even in this case it is not possible directly to calculate volumes for the constituents of the molecule if the chemical formulae are of the same type throughout; when, however, the formulae differ in type a solution may be possible.

The availability of analytical methods that utilize the very intense and bright X-rays from synchrotron radiation sources has fundamentally changed the way in which geoscientists, environmental scientists and soil scientists study complex environmental samples and decipher the chemical and biological processes that impact the speciation, transport and potential bioavailability of environmental toxins (Brown et al., 2006). Such samples are often mixtures of crystalline and amorphous phases in particle-sizes ranging from cm to nm, adsorbed metal ions and organic molecules, natural organic matter, microbial organisms, algae, plant materials and aqueous solutions. The processes that affect the chemical forms and environmental fate of contaminants in such mixtures range from surface adsorption, desorption, precipitation and dissolution reactions, often involving a combination of hydrolysis, ligand exchange and electron transfer, to biological interactions in which microbial organisms, algae or plants interact with mineral surfaces and environmental contaminants.