Trigonal trisoctahedron, a trisoctahedron each face of which is an isosceles triangle.
Trigonal pyramid {hkk}, consisting of the three faces which correspond to the three upper or the three lower faces of a rhombohedron of the holosymmetric class.
The general form {hkl} is a trigonal pyramid consisting of three faces at one end of the crystal.
All the prisms are trigonal prisms; and perpendicular to these are two pedions.
The trigonal pyramids of the last class are here trigonal bipyramids (fig.
Those with a triad axis are grouped together in the rhombohedral or trigonal division, and those with a hexad axis in the hexagonal division.
All other forms, in which the faces are neither parallel nor perpendicular to the triad axis, are trigonal pyramids.
In the rhomobohedral or trigonal division of the hexagonal system there are seven symmetry-classes, all of which possess a single triad axis of symmetry.
These small modifying faces, etching figures, and microscopic tests show that quartz is really trigonal in spite of the common occurrence of simple six-sided outward forms.
Often crystallizes in the trigonal system almost always as six-sided prisms capped by six-sided pyramids, which are really combined three-sided forms, often with alternate corners modified by small faces.
Commonly as crystals in the trigonal system in both long and short prismatic forms, as shown by Figure 75m, with opposite ends not unlike.
Cones large, cylindrical or long oval, with large scales of trigonal form, and not elongated but lying close to the surface.
Orton also noticed the absence of the trigonal form, which belongs to the spores of many Lepidodendra, though this is not a constant character.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "trigonal" in a variety of sentences. We hope that you will now be able to make sentences using this word. Other words: cuneiform; deltoid; triangular; trident; tripartite
