15. “Anorthoclase,” Frederiksvérn, Norway. 
THE MINERALOGRAPHY OF THE FELDSPARS 273 
(Specimen 98T.) 
Microscopic examination, thin section: There is a faint suggestion of 
microclinic twinning on a very fine scale. Some areas appear to be 
entirely free and have slightly different optical characters. There are 
veinlets of oligoclase and stringers of soda microcline but they are too 
small for quantitative measurements. 
Extinction angles, crushed fragments: 
Untwinned......... (ne) eo Se ELLOy 
(Com)its teens 2.00 
awantaedy,'.. < Seke 2c. ls (GIO) eee: Boke 
(Con) ier ee. eee Ook) 
It follows from examination of the chart, Figure 8, that the untwinned 
fragments are orthoclasic, that is monoclinic (?), while the twinned pieces 
are microclinic, triclinic (?). 
Inferred composition: 
I feldSmai was mya Marae ae Genes 45 
INasteld/spanpe sya ttc assis desist 5 53 
Carfeldspari: Wis wensadecis sae 2 
CHEMICAL AND MICROSCOPIC ANALYSES 
SiO. Al.O3 Fe.03 CaO K.0 Na.O H:.0 Total 
HM eect cacvareiey ncaa a! « 65.19 | 19.99 63 .48 | 7.03 | 7.08 .38 | 100.78 
Dé 0p OEE GOROSM IETS 7.70 seen: 587 || 7508 || ©oF4 Jocooae 99.44 
K-feldspar Na-feldspar Ca-feldspar 
Es o SHO Nectar 44.09 57.65 2.26 
Bence oD RD OGRAG 44.41 53.82 77 
MVIIcrOSCOpic....-.... 45.0 53-0 2.0 
Classification: Anorthoclase, potentially eutectoperthite.? 
16. “Orthoclase,’ East DeKalb, St. Lawrence County, New York. (Specimen 
995.) 
Microscopic examination, thin section: 
A typical microcline micro- 
perthite, not orthoclase. 
A few inclusions of apatite, calcite, phogopite, 
and hematite. 
The latter due to exsolution. 
Extinction angles, crushed fragments: 
Potash phase........ (Ciito))) een 8.0° 
(Gon) ee eras soe TeOw 
Sodayp ase cee ery (Oro) Meek oe 10.0° 
(oro tO ae hi. 5 
t Analyses t and 2. Carl Hintze, Handbuch der Mineralogie. 
Kalifeldspath, 
CCXXIX and CCXXX, 1414, 1802. 
