Biotite flakes: alteration by chemical and biological treatment.
Biotite alteration under acid conditions proceeds differently from the generally accepted pathway of transformation to vermiculite in which hydrated cations cause interlayer expansion, resulting in a dark-colored peripheral band on mica particles. Acid solutions of synthetic or biologic origin remove octahedral ions, leaving a fragile matrix of amorphous material.
Boyle
J R
JR
Voigt
G K
GK
Sawhney
B L
BL