Plagioclase Thin Section

11 minerals in thin section university of north carolina 12 minerals in thin sections humboldt state 13 online mineral museum 14 qut mineral atlas 15 ruff info 16 ucla petrography thin sections 17 www mincryst.

Plagioclase thin section. Home rocks and minerals plagioclase feldspar thin section reference url share. Search for plagioclase using. You can find the explanation on the plagioclase feldspar page.

Plagioclase is series of framework silicate minerals in feldspar group. Small 250x250 max. Add tags comment rate.

The composition of a plagioclase feldspar is typically denoted by its overall fraction of anorthite an or albite ab and readily determined by measuring the plagioclase crystal s refractive index in crushed grain mounts or its extinction angle in thin section under a polarizing microscope the extinction angle is an optical characteristic and varies with the. Albite twins are prominent and some small pericline twins can also be seen. Can be confused with quartz if there is no twinning however the optic axis figure will resolve this.

This twinning is the most characteristic identifying feature of plagioclase and makes its identification easy when present. Plagioclase unzoned in a hornblende diorite. Plagioclase feldspar thin section view description.

In thin section or grain mount the general lack of pleochroism and the twinning are good indicators. The series ranges from albite to anorthite endmembers with respective compositions naalsi3o8 to caal2si2o8 where sodium and calcium atoms can substitute for each other in the mineral s crystal lattice structure. It s helped a surprising number of people keep their feldspars straight.

Albite in hand sample. The presense of parallel striae on cleavage surfaces distinguishes plagioclase from k feldspar. Ateration to fine grained material typically occurs along fractures twin planes or cleavages.