Potholes are roughly cylindrical or bowl-shaped depressions IN ROCKS OF RIVER AND inshore platforms that are ground out by the swirling action of sand, gravel, pebbles, andboulders associated with wave action.
Penetration Twins - have an irregular composition surface separating 2 individual crystals. These are defined by a twin center or twin axis. Shown here is a twinned crystal of orthoclase twinned on the Carlsbad Law with [001] as the twin axis.
Contact Twins - have a planar composition surface separating 2 individual crystals. These are usually defined by a twin law that expresses a twin plane (i.e. an added mirror plane). An example shown here is a crystal of orthoclase twinned on the Braveno Law, with {021} as the twin plane.
•Form: Primatic crystals; at times as massive and compact, granular grains• Colour: Shades of green (olive green) to black•Streak: colourless• Lustre: Vitreous; transparent to translucent•Fracture: conchoidal•H: 6-7•Sp. G: 3.2 (Fo) to 4.3 (Fay)