270 HAROLD L. ALLING 
rr. “Microcline-Amazonstone,”’ Mineral Hill, Pennsylvania. (Specimen 964.) 
Microscopic examination, thin section: Under the microscope it is readily 
seen that there are two generations of perthitic intergrowths. The 
potash phase, which is intergrown with a soda-rich feldspar, is in turn full 
of secondary blebs of a soda phase. This may be explained as due to 
the fact that complete separation of the two phases was accomplished at 
relatively high temperatures, while the subsequent separation has taken 
place at more moderate temperatures. The latter phenomenon is probably 
due to decreased solubility as determined by the slope of the solubility- 
saturation curve, line AZ in Figure 4. The fact that the “secondary” 
blebs of potash feldspar in the original member, rich in soda, are not seen, 
even under high magnifications (950 diameters), testifies to the nearly 
vertical character of the corresponding curve, BM in Figure 4. 
Extinction angles, crushed fragments: 
Potash phases ee oe (oro) \er Tink 
(Cons nce 16.9° 
Sodasphasea eis are (CRO) acct eee 19.0 
(COT) tem ees 4.8° 
QUANTITATIVE MICROSCOPIC ANALYSIS 
| 
Phase Phase Aaa ea Phase pees Nea oe SiO: 
85 -(|f9° Sodasmicro, || 80.0) si7onimes o 2 ui 
< K-feld. \10 Albite 2 BON OSHOm MeO 
Perthite : 
citnahe Na-feld 19.6 |(19.6 | Albite x 2.0152 0n MEO) 
@Quantzeenerre Quartz oF lia eee ee es Wich cllendia co" 5 0'¢ «oc 100 
(K-feld. 8 j Soda micro: |.57 6) |\s129em meme 
Perthite..... { q |Albite 2 12) || eo 2) ie 
| Na-feld. 19.6 (Albite x 6 | 18.6 4) 
@uantzaneeer Quartz... WA Ne ba bas oe we lL BOs eS | eee 4 
ATG tall suka setts coy scee opel estes cucees Vea cael ease here eee eR Bal | Yeinb |) 2.8 4 
Classification: 
Popular: Microcline microperthite 
Technical: Microcline hypoperthite. 
12. “Orthoclase,”’ near Unionville, Chester County, Pennsylvania. (Speci- 
men 990.) 
Microscopic examination, thin section: Typical microcline microperthite 
with inclusions of diopside, quartz, and untwinned feldspar thought to be 
anorthoclase. 
