Proceedings of the United States National Museum . biaxial, negative, 2V small,r>v weak, |3= Lying on the broad face be-tween crossed nicols these show the emergence of theoptic normal with a very small inclination, of but adegree or two, of the extinction to the edge, and showa faint suggestion of twinning. When crushed theyexhibit two cleavages, one perpendicular to the opticnormal or parallel to the plane of the optic axes (010), and a second,nearly as perfect, parallel to the front pinacoid (100) which is per-pendicular to the obtuse bisectrix. This makes the optical orientation,
Proceedings of the United States National Museum . biaxial, negative, 2V small,r>v weak, |3= Lying on the broad face be-tween crossed nicols these show the emergence of theoptic normal with a very small inclination, of but adegree or two, of the extinction to the edge, and showa faint suggestion of twinning. When crushed theyexhibit two cleavages, one perpendicular to the opticnormal or parallel to the plane of the optic axes (010), and a second,nearly as perfect, parallel to the front pinacoid (100) which is per-pendicular to the obtuse bisectrix. This makes the optical orientation,if the crystals are set with their elongation vertical, Y = &, Z = a,Xac=0°-2°. Another specimen showing the larger crystals or rather bundles ofcrystals in parallel position, furnished material for a partial analysiswhich furnished the results of column 1 of the following table. Incolumn 2 are given the figures of the theoretical composition of stil-bite, taken from Dana, and in column 3 the analysis by Thugutt andRosicky of *^. Fig. 24.—Stibite ofepidesminehabit boundedonly by threepinacoids. 2= Appandix III, Dana Syst. Min., p. 27. PETEOLOGY AT GOOSE CREEK SHANNON. 75 Constituent. SiO^ AI0O3 CaO MgO K2O NaaO H2O+110°CH2O-110°CInsoluble Total GooseCreek. 56 Theory. 30 7. 70 16. 002. 32 99. 16 100, 00 Epides-mine. 56. 88 18. 69 .44 100. 98
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Keywords: ., bookauthorun, bookcentury1800, bookdecade1870, booksubjectscience
