Читать книгу Earth Materials онлайн
140 страница из 155
Hexagonal system (hexagonal division) forms
Common crystal forms in the hexagonal system include 6–12‐sided prisms, dipyramids, and pyramids. Pinacoids and pedions are also common. Some selected examples of common crystal forms and minerals in the hexagonal system are illustrated in ssss1 and ssss1.
Trigonal system (hexagonal system, trigonal division) forms
Common closed crystal forms in the trigonal system include the six‐sided rhombohedron, the 12‐sided scalenohedron, six‐sided hexagonal dipyramids and three‐sided trigonal pyramids. Three‐ and six‐sided prisms, and pinacoids and pedions are also common. Many forms common in the hexagonal division also occur in trigonal crystals, but not vice versa. Common crystal forms and representative minerals in the trigonal crystal system are summarized in ssss1 and ssss1.
ssss1 Common crystal forms in the hexagonal crystal system (hexagonal division): (a) hexagonal prism closed by a basal pinacoid, (b) hexagonal dipyramid.
ssss1 Common hexagonal crystal forms and associated hexagonal and trigonal minerals.