Page 84 - A Practical Introduction to Optical Mineralogy

SILICATE MINERALS FELDSPAR GROUP
Alkali feldspars • h lh~tt'htse-low albite series Or,oo-85 orthoclase
There is a continuous series from K-feldspar (KA1Si 3 0 8 ) to albite Or 85-20 orthoclase cryptoperthites
(NaA1Si 30 8 ) for high and low alkali feldspars. Or20-o low albite

Sanidine-high albite series Ab 0 - Ab 63 sanidine IJ, •m·lln low albite series Or,oo-n microcline
anorthoclase microcline cryptoperthites
Ab 63 - Ab 90 Or •2-zo
high albite low albite
Ab. 0- Ab 100 Or zo- o

Orthoclase Microcline
High sanidine c Low sanidinc c
'I I c I
I I 13 I I I
I l I I
I lXII I 00 1 I I
I I I

- -b ='I

/
/
/
/ Cl./
/
Cl.

13
I
I
I
001 /
I

High albite

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