Trigonal crystal system,

Hematite crystallizes in the trigonal crystal system, space group R3c = D d. and is... 

Triclinic crystal system, 75, 78 Trigonal bipyramidal (TBP) structure, 480-483 Trigonal crystal system, 75, 78 Trigonal hybrid, 150-153 Trigonal prism, 489-491 Trimethylborane, 205 Trinegative ions, 332-333 Trinuclear clusters, 813-815 Tropylium complexes, 683-684 Tutankhamen, 458 Twist angles, 490... 

Rhombohedral unit cell Figure 1.26) is a special unit cell that is allowed only in a trigonal crystal system. It contains two additional lattice points located at 1/3, 2/3, 2/3 and 2/3, 1/3, 1/3 as shown by the ends of the two vectors inside the unit cell, which results in a total of three lattice points per unit cell. 

In hexagonal and trigonal crystal systems, the fourth index is usually introduced to address the possibility of three similar choices in selecting the crystallographic basis as illustrated in Figure 7.5 7. In addition to the unit cell based on the vectors a, b and c, two other unit cells, based on the vectors a, -(a + b) and c, and -(a + b), b and c are possible due to the six-fold or the... 

Figure 1.37. Three possibilities to select the crystallographic basis in hexagonal and trigonal crystal systems and the family of (1120) crystallographic planes in the hexagonal crystal system. Indices are shown in the unit cell based on the vectors b and c. Three additional symmetrically related families of planes have indices (1120), (1210) and (2110) in the same basis and we leave their identification to the reader.

Table 2.14. Reflection conditions for the trigonal crystal system. There are no space groups with a unique set of reflection conditions.

Trigonal crystal system the holohedric group Dja, and those sub-groups which do not belong to classes 1 and 2 Dgd Ds, Cav Ss, Cg... 

The rhombohedral (or trigonal) crystal system is one of the seven lattice point groups, named after the two-dimensional rhombus. In the rhombohedral system, the crystal is described by vectors of equal length, of which all three are not mutually orthogonal. The rhombohedral system can be thought of as the cubic system stretched diagonal along a... 

Ba3SieOi2N2 crystallizes in the trigonal crystal system with the space group of P-3 (no. 147). The crystal structure of Ba3Si60i2N2 has fused rings-sheets,... 

Since 3m and 6/mmm are included in the same point lattice, they are sometimes subsumed into the hexagonal crystal family. So there are seven crystal systems but six crystal families. Note further that rhombohedral symmetry is a special case of centering (/J-centering) of the trigonal crystal system and offers two equivalent possibilities for selecting the cell parameters hexagonal or rhombohedral axes (see Table 1.3-4 again). 

The other carbonate mineral in common use as a filler is dolomite calcium magnesium carbonate (CaC03. MgC03). It is in the trigonal crystal system and is usually found as rhombohedral crystals with curved composite faces. Dolomite is harder (3.5), denser (2.85), and slightly more acid resistant than calcite, bnt in general, the mineral properties and properties in a polymer are similar. 

PbSbjOs Related mineral form Trigonal crystal system... 

The trigonal crystal system can be defined by hexagonal or rhombohedral axes, denoted by (H) and (R), respectively. 

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