390 Penfield and Sjperry — Triclinic Feldspars with 



Si0 2 51-85 



A1 2 3 4-52 



FeO :. 13-26 



CaO 1-09 



MgO 29-28 



100-00 

 Giving the ratio of K^O to Si0 2 = *93 : -86, which corresponds- 

 well with the mineral enstatite, although in this case much of 

 magnesia is replaced by iron. The soluble portion consisted of 

 iron with a slight trace of nickel, which tends to show that the 

 nodule contained some metallic particles which it was impossi- 

 ble to extract with the magnet. During the digestion in acid, 

 as no sulphuretted hydrogen could be detected, we infer the 

 non-existence of sulphides in the nodule. 



The total mineral was also analyzed with the following 

 results : 



Si0 2 49-96 



A1 2 3 4-75 



FeO 15-97 



CoO + NiO trace 



CaO 1-15 



MofO 28-15 



99-98 

 This meteorite then is a lithosiderite poor in metal, the 



metallic portion not exceeding 16 per cent of the mass. The 



stony part is probably anorthite and enstatite. 

 Chem. Lab. IT. S. G. S., Washington, D. C, Aug. 26, \m*l. 



Art. XLIY. — Triclinic Feldspars with twinning striations on 

 the hrachypinacoid ; by S. L. Penfield and F. L. Sperry. 



On looking over the cleavage specimens of plagioclase feld- 

 spar in the collection of Professor Geo. J. Brush, especially 

 those which would be classed as albite or oligoclase, we were 

 surprised to find how many of them showed striations due to- 

 twinning on i-% (010), in addition to the ordinary striations on 

 the basal plane. These striations on the brachypinacoid have 

 not been very prominently noted in text-books on mineralogy,, 

 and we have thought that it would be of interest to study them 

 in connection with the chemical analyses of the feldspars. We 

 are largely indebted to Professor G. vom Eath for our knowl-. 

 edge of the twinning striations on i-% of the plagioclase feld- 

 spars. He showed* that they resulted from twinning accord- 

 * Jahrb. f. Mm.,-18?8, 689. 



