Twinning In Thin Section

If only partial removal of the original mineral and only partial replacement by the new mineral has taken place then it is possible to have a the space once occupied entirely by the original mineral be.

Twinning in thin section. You can find the explanation on the alkali feldspar page. In a the polysynthetic twinning albite law of plagioclaseis evident in the zebra effect of adjacent twins having slightly different shades of first ordergrey to white colours. This is called incomplete extinction or sometimes birds eye maple extinction.

If no twinning is mentioned then the phenomenon is not common in thin section if no twinning is mentioned then the phenomenon is not common in thin section. In such case it would be called an oligoclase a subtype of plagioclase it has already been mentioned that the colors of plagioclase even if the thin section is thicker than usual seemed to indicate a. A few notes about twinning or other internal features of crystals may be given.

Damage produced during thin section grinding causes speckles of light in the biotite where the crystal lattice has been deformed. In this case the thin crust of the new mineral will have casts of the form of the original mineral. Tartan plaid or plaid twinning is a combination of albite and pericline twinning.

Rare spinel cyclic twin from pyin oo lwin district mandalay division myanmar. Polysynthetic twinning occurs when three or more individuals are repeated alternately on the same twinned plane. As far as i know this happens only in basal sections.

In thin section alkali feldspar grains often look like they re sprinkled with dirt ppl or tiny confetti xpl. There is one thing that i can t explain though. Minerals with similar appearance may include plagioclase although it can be distinguished by the distinctive twinning in crossed polarized light and cleavage in plane polarized light and cordierite although it can be distinguished by twinning or inclusions in the grain.

Twinning is the symmetric intergrowth of two or more crystals of thesame mineral and commonly is revealed in thin section by the differentcrystals of the same mineral having different extinction positions or differentinterference colours. I found this beautiful euhedral pyroxene crystal in thin section today. It is the dead giveaway of microcline.