THE MINERALOGRAPHY OF THE FELDSPARS 263 
EXAMPLES OF POTASH-SODA FELDSPARS 
1. “Orthoclase,” “Adularia coated with chlorite,’ Scopi, Switzerland. (Speci- 
men 988.) 
Microscopic examination, thin section: Clear, untwinned potassic feldspar. 
Extinction angles, crushed fragments: 
(or0) Shon 
(cor) °.4° 
Inferred composition, considering potash component: 
Kefeldsparseen eee g2.0 
INa-teldspar.. 22... 6.0 
@azfeldspareeoee 250 
This is one of the very few specimens examined to which the term “‘ortho- 
clase” can be assigned in accordance with the nomenclature here adopted. 
Classification: True orthoclase. 
2. “Chesterlite,” Poor House Quarry, West Chester, Pa. (Specimen 997.) 
Microscopic examination, thin section: Broad phantom twinning, suggest- 
ing microcline. 
Extinction angles, crushed fragments: 
(o10) 6.0° 
(oor) WO) 
Inferred composition, considering the potash component: 
Keteldsparaeerc see: 83.0 
INa-teldspars same ce 14.0 
@a-feldspars: a0. 4-4- 3.0 
CHEMICAL AND MICROSCOPIC ANALYSES 
SiO: ALO; K.0O Na:O Ign Fe.0 CaO MgO Total 
yi. 5 See ene 64.97 | 17.65 | 14.02 | 1.69 .65 .50 .50 .27 | 100.36 
K-feldspar Na-feldspar Ca-feldspar 
Chemical... . 82.8 14.2 Lee BO 
Microscopic. . 83.0 14.0 BES 
Classification: Popular and technical: Soda microcline. 
Analysis. James D. Dana, System of Mineralogy. Miicrocline 5. Hintze, 
Handbuch der Mineralogie. ‘“‘Orthoclase and Microcline Kalifeldspath,’’ CCXCII. 
