THE MINERALOGRAPHY OF THE FELDSPARS 265 
CHEMICAL AND MICROSCOPIC ANALYSES 
SiO. Al.O; Fe.0; CaO Na.O K.0 Ign Total 
5000 0.00 CE nen OS SON LOMSON eeaeeieieLesS 6&5 || 2207 llosooaell @@otert 
10690 000 65.23 | 20.09 oF® lor ocooll Boe) || wir Co -36 | 99.99 
K-feldspar Na-feldspar , Ca-feldspar 
30.0 0 OG SSO Eran 85.8 5.3 8.9 
2 9 0.0 0 ORO a nae 80.2 19.8 Al Soaecattee ievrooaset's 
Microscopic......... 76.0 16.5 7.5 
Classification: 
Popular: Microcline microperthite 
Technical: Microcline hypoperthite. 
Analysis r. Collection of A. A. Robbins, now on exhibition in the New York 
State Museum, Albany, New York. 
Analysis 2. E.S. Bastin, U.S. Geol. Surv. Bull. 420, p. 24. 
. “Microcine Amazonstone,’ Amelia Court House, Amelia County, Virginia. 
(Specimen 992.) 
Microscopic examination, thin section: Microclinic microperthite. 
Some of the intergrowths of the potash and soda phases have an appear- 
ance as though they were primary, due to the freezing of the eutectic 
mixture. ; 
The albite-oligoclase occurs in stringers which vary in thickness and are 
not continuous. The “linkage” areas between these blebs are charac- 
terized by a much finer Scotch-plaid type of twinning in the soda micro- 
cline which appears to be akin to anorthoclase. These areas then may 
be regarded as a supersaturated crystalline solid solution changing to 
microperthite by exsolution. 
Extinction angles, crushed fragments: 
Potash phase........ (ONO) ese eres 6.4° 
(Geld) See aie aes Tania 
Soda phasemey sae (GIO) a lascan e 2 ROg 
(om) epee ends BO 
Inferred Composition Potash Phase Soda Phase 
K-feldspar........... 80.0 2.0 
Na-feldspar.......... 18.0 88.0 
Ca-feldspar.......... 2.0 10.0 
