Quartz, Japan-Law Twin

This type of quartz Japan-law twin is referred to as a "closed twin" or very close to it. They are referred to as closed when the re-entrant angle is very small so as to appear merely as a notch, compared with "open" twins with long, quartz crystal members. This on is a frosty, very flattened twin, with just a notch for a re-entrant angle.