Two intergrowing or twinned quartz crystals
Diagram of the typical quartz crystal, p prism faces, l left hand rhombohedron, r right hand rhombohedron
A quartz crystal on which the left hand rhombohedron is represented by small faces while the right hand rhombohedron has large faces
Plate 14
Crystal forms of hematite, A the rhombohedron with the edges beveled; B the tabular form, resulting from the excessive development of the two o faces opposite each other
A typical crystal of magnetite