Crystal system: Monoclinic
Twinning: simple, lamellar, common
Cleavage: two good at about 60 or 120o
Relief: moderate, moderate to high
Occurrence: metamorphic rocks
It is often more convenient in pottery thin-sections to group the amphibole group together.
They can be identified collectively by the distinct cleavages and it is probably preferable in most cases to simply
say whether the inclusion is pleochroic, and if so what is the nature of the pleochroism, or that it is not pleochroic at all.
This is preferable to unreliable identifications, the most common being identifying a red pleochroic amphibole as the relatively
rare oxyhornblende, when it is more likely to be an ordinary green-pleochric amphibole which has been altered in the firing.
Minerals in the Amphibole group are: