Earth Materials. John O'Brien

Читать онлайн книгу.

Earth Materials - John  O'Brien


Скачать книгу
i, 1A6, 6A2, 7m Ditrigonal–dipyramidal 6m2 1A6, 3A2, 3m Dihexagonal–pyramidal 6mm 1A6, 6m Hexagonal–trapezohedral 622 1A6, 6A2 Hexagonal–dipyramidal 6/m i, 1A6, 1m Trigonal–dipyramidal ModifyingAbove 6 With bar 1 normal upper A 6 overbar Hexagonal–pyramidal 6 1A6 Hexagonal (rhombohedral or trigonal) Hexagonal–scalenohedral ModifyingAbove 32 With bar slash normal m 1 normal upper A 3 overbar, 3A2, 3m Ditrigonal–pyramidal 3m 1A3, 3m Trigonal–trapezohedral 32 1A3, 3A2 Rhombohedral ModifyingAbove 3 With bar 1 normal upper A 3 overbar Trigonal–pyramidal 3 1A3 Orthorhombic Rhombic–dipyramidal 2/m2/m2/m i, 3A2, 3m Rhombic–pyramidal mm2 1A2, 2m Rhombic–disphenoidal 222 3A2 Monoclinic Prismatic 2/m i, 1A2, 1m Sphenoidal 2 1A2 Domatic m 1m Triclinic Pinacoidal ModifyingAbove 1 With bar i Pedial 1 None Schematic illustration of relationship between (a) atomic packing, (b) a unit cell, and (c) octahedral coordination polyhedra in halite (NaCl).

      Source: Wenk and Bulakh (2016). © Cambridge University Press.

Schematic illustration of the 14 Bravais lattices and the six (or seven) crystal systems they represent.

      Source: Courtesy of Steve Dutch.

Crystal system Unit cell edge lengths Unit cell edge intersection angles Bravais lattice types
Isometric (cubic) (a = b = c) Preferred format for edges of equal length is (a1 = a2 = a3) α = β = γ = 90° Primitive (P) Body centered (I) Face centered (F)
Tetragonal (a1 = a2 ≠ a3) or a = b ≠ c α = β = γ = 90° Primitive (P) Body centered (I)
Hexagonal (hexagonal) (a1 = a2 ≠ c) (a = b ≠ c) (α = β = 90o ≠ γ = 120°) Primitive (P)
Hexagonal (trigonal or rhombohedral) (a1 = a2 = a3) α = β = γ ≠ 90° Primitive (P)
Orthorhombic a ≠ b ≠ c (α = β = γ = 90°) Primitive (P) Body centered (I) End centered (A, B, C) Face centered (F)
Monoclinic a ≠ b ≠ c (α = γ = 90° ≠ β) Primitive (P) End centered (C)
Triclinic a ≠ b ≠ c (α, β, and γ ≠ 90°) Primitive (P)

      Imagine yourself, if you can, the crystals on a web site, in a mineral shop or a museum. Such crystals are partially or completely bounded by planar crystal faces that are produced when minerals grow. Many other mineral specimens are partially or completely bounded by flat, planar cleavage faces produced when minerals break along planes of relatively low total bond strength. The shapes of the crystals,


Скачать книгу