60 Mr Alger on New Localities of Bare Minerals. 



specimens, which eventually proved to be this mineral, were labelled 

 Stilbite ; but their appearance was so peculiar, that I questioned at 

 the time whether they had been correctly designated, and determined 

 to examine them carefully at my earliest convenience. I have since 

 received two other specimens, better characterized than the first, from 

 Mr Johnson. The crystals are in a geode form, implanted on cal- 

 careous spar, and associated with silver-coloured mica and a few 

 scales of Oligisto-magnetic iron-ore. They are of a wax or honey- 

 yellow colour, have a waxy lustre, and the smallest individuals are 

 translucent. They are brittle, breaking with an uneven fracture, 

 have none of the foliated structure of Stilbite, and afford no indica- 

 tions of cleavage ; hardness superior to that of Stilbite, and equal 

 to that of Chabasite. Their surfaces are roughened or pitted, so as 

 to reflect no image by which they could be subjected to measurement 

 by the goniometer. Before the blowpipe, a fragment of the mine- 

 ral swells and intumesces slightly, like the Bohemian and Ferroe 

 Chabasite, and fuses into an opaline, blebby bead ; at the moment of 

 ignition, in the outer flame, it gives out a beautiful green phospho- 

 rescence, which I have also noticed, in a less degree, in the phaco- 

 lite from Ireland. It is soluble in hydrochloric acid. The crystals, 

 at first sight, appear to be rounded, and to have no determinate form ; 

 but, on closer examination, some of the smaller and more isolated 

 ones are found to be nearly perfect double six-sided pyramids, pre- 

 cisely similar to the phacolite from Bohemia, differing from it only 

 in colour and lustre. I cannot doubt that, like that mineral, they 

 are secondaries to a primary rhombohedron, probably of the same 

 measurements, and are also identical with it in composition. The 

 absence of well-defined cleavage is unfortunate, but this is a defect 

 which applies equally to the foreign mineral. Nor is the rhombo- 

 hedral cleavage of ordinary chabasite, of which phacolite is by many 

 supposed to be only a variety, by any means easily determined ; in 

 fact, Sir David Brewster has suggested, from optical investigations, 

 whether the primary form of chabasite be not a prism. 



Is Phacolite a variety of Chabasite^ or distinct from it P-— Tam- 

 nau, of Berlin, in his very complete little essay on chabasites, has 

 given very good reasons for uniting the two ; while Breithaupt has 

 maintained them to be distinct. The primary rhombohedron of 

 phacolite, according to Breithaupt, is P on P, 94°, that of chabasite 

 P on P, 94° 24^ Phillips makes the last 94° 46'. The analyses 

 of Anderson and Bammelsberg would seem, at first, to shew a 

 marked difference in their composition, a difference which is also 

 shewn by the different analyses of common chabasite, resulting in 

 varieties having different formularic expressions. For example, Aca- 

 ■diolite contains three per cent, more of silicic acid than common Cha- 

 basite, and is a tersilicate of lime and the other isomorphous bases, 

 instead of a bisilicate of the same bases. The mineralogical formula 

 of Acadiolite is, 3 Al Si^ + (Cal, N, K), Si^ + 6 Aq., while that of 



