Allanite, a rare-earth bearing member of the epidote group, occurs as an accessory mineral in granitoid rocks.  It is commonly euhedral to subhedral and has very high relief relative to quartz and feldspars with which it occurs.  Most examples are  strongly coloured and pleochroic in shades of yellow and brown (compare A and B, rotated 90 degrees to one another), and many grains are zoned.  Interference colours are upper first to second order, but typically masked by the strong absorption (C).  Allanite can contain U and Th, the decay of which results in radiation damage of the allanite and surrounding minerals.  Minerals with their crystal structures damaged by such internally produced radiation are termed “metamict” and one effect of this is expansion of the grain.  This is the cause of the radiating cracks in the quartz and feldspar around the allanite in D.  Strongly metamict allanite has lower relief and interference colours than does fresh allanite. A-C are from the Robertson River Batholith, Virginia and D is from the Tunk Lake Pluton, Maine.  All images are 2.2 mm across.  A, B, D ppl, C x-nicols.