418 



SCIENCE 



[N. S. Vol. XXXI. No. 794 



remains an uncorrected labradorite angle of 

 — 29° 55'. I apply to these proportional cor- 

 rections, namely, for albite +1°, giving the 

 true albite angle ^ -|- 19° ; and for labradorite 

 a correction of — 1° 30', giving true angle 

 = — 31° 25'; which corresponds to a labra- 

 dorite formula of albite 1, anorthite 4. A mean 

 of the extinctions on opposite sides of a twin- 

 ning plane in a typical labradorite crystal 

 gave — 31° 18', which agrees with the previous 

 determination of Ab^An^. The crystals, 1 or 

 2 mm. wide, and 5 to 10 mm. long, form a 

 pretty closely parallel ophitic structure. A 

 few crystals show Carlsbad twinning. 



The ground-mass between the parallel feld- 

 spars is made up of a micro-crystalline mesh 

 of the same material with very fine crystals 

 (0.01 mm.) of a dark green pleochroic mineral, 

 which appears to be biotite, and with equally 

 minute crystals of magnetite, together with 

 some titanite. The crushed mineral is almost 

 entirely decolorized by boiling hydrochloric 

 acid. Irregular larger masses of ilmenite with 

 titanite borders, and masses of green biotite 

 (1 to 2 mm. in diameter) in fine crystals, 

 pleochroic with green and brown colors, com- 

 plete the inclusions within the ground-mass. 

 Dr. G. F. Loughlin, who helped me identify 

 some of the minerals, is of the opinion that 

 the rock has been " contact-metamorphosed, 

 presumably by granitic intrusion, which set 

 free heated water with potash and fluorine. 

 These changed the original ferromagnesian 

 minerals into biotite, and a little of the ilmen- 

 ite and feldspar into titanite, garnet, sericite 

 and secondary albite." The material is com- 

 pletely crystalline and has a decidedly fresh 

 look, the fracture sparkling with minute 

 crystalline facets. 



Frank W. Very 



Westwood, Mass. 



the norwood meteorite (?) 

 As Professor Very, in Science of January 

 28, 1910, has seen fit to place on record the 

 discovery of a stone claimed to be a meteorite, 

 but unlike any meteorite hitherto known, a 

 petrographic description of the stone may be 

 of interest. The writer has discussed the 



matter with Professor Very, and at his sug- 

 gestion, viewed the stone (on exhibition in 

 Austin & Stone's Dime Museum), visited the 

 spot where it was discovered and examined a 

 thin-section which Professor Very furnished. 



The stone may be called, megascopically, a 

 basalt-porphyry. Its color on fresh fracture 

 is nearly black, its luster rather dull. The 

 ground mass is extremely fine-grained to fel- 

 sitic. It is sprinkled with tabular pheno- 

 crysts of labradorite (about 30 per cent, of the 

 rock) and with a few small grains of ilmenite. 

 The natural surface is gray. There are no no- 

 ticeable oxidation effects, but the ground mass 

 has suiiered marked corrosion, such as is pro- 

 duced by swamp waters, leaving the plagio- 

 clase phenocrysts in pronounced relief. The 

 latter are greenish-gray, tabular with rounded 

 corners and measure up to 12 or 15 mm. in 

 length. They show in general a parallel ar- 

 rangement, or flow structure. 



The slight salty odor of the stone men- 

 tioned by Professor Very was not noted, but 

 may well have been lost in the characteristic 

 atmosphere of the dime museum. 



The minerals noted in thin section are 

 labradorite and ilmenite, both as phenocrysts 

 and in the ground mass, biotite, titanite, gar- 

 net and sericite, with a little albite (?), epi- 

 dote and kaolin. The ground mass consists 

 chiefly of plagioclase and biotite. The lab- 

 radorite phenocrysts show excellent Carlsbad 

 and albite twinning. Both the phenocrysts 

 and the feldspars of the ground mass are but 

 slightly kaolinized, but are partially replaced 

 by garnet, titanite and sericite. The garnet 

 forms irregular grains fingering into the 

 feldspar or the ground mass. The titanite 

 forms rings around ilmenite grains, in some 

 instances fingering into feldspar crystals. The 

 sericite is sprinkled through the feldspar 

 phenocrysts and the ground mass in typical 

 minute flakes, single or in aggregates. The 

 biotite is flnely disseminated throughout the 

 ground mass and in a few places is bunched 

 into fine-grained aggregates, strongly sug- 

 gesting replacement of some femic pheno- 

 cryst. No trace, however, of any other femic 

 mineral was noted. Only two small grains of 



