Figure 46 (a) An amphibole with a prismatic crystal form (shorter crystal is 3 cm long). (b) A plane-polarised light image of an amphibole in a metamorphic rock called amphibolite. This shows a basal section in which two cleavage planes intersect at about 120°. This amphibole has a strong pale greyish-green turning to dark greyish-green pleochroism (field of view 2 mm across). (c) The same field of view as in (b) between crossed polars. Although the amphibole has second-order interference colours, they can be masked by the strong body colour of the mineral - i.e. its colour in plane-polarised light.