I) bounded by the two faces of the basal **pinacoid** (c) and the four faces of the prism (m); the angle between the prism-faces (mm) is 78° 23', whilst that between c and m is go.

R is bounded by the basal **pinacoid** c (ooi) parallel to which is the perfect cleavage, the clinopinacoid b ((D10) parallel to the plane of symmetry, and the pyramids m (221) and o (112).

The Helena crystals are of tabular habit, being composed of the basal **pinacoid** with a very short hexagonal prism, whilst at Yogo Gulch many of the crystals affect a rhombohedral habit.

I are the basal **pinacoid**, a {oor}, and two square pyramids, b { 'or } and c { 2011.

2 is a tabular crystal in which the basal **pinacoid** (o) predominates.

2 and 3 are bounded by the domes d and f and the basal **pinacoid** c; fig.