The corners of the calcite rhombohedron
, however, are not all the same.
Phantoms are not evident in any crystals, but in some cases the separate rhombohedrons
in parallel alignments differ slightly in color.
(3) Formation of tiny sheaf-like sprays of black goethite together with small amethyst crystals--quartz (II)--in "skunk" stripes upon the calcite rhombohedrons
Forms like the scalenohedron can be generated by stacking tiny rhombohedrons
in a certain way.
Galena forms tiny rounded crystals, and calcite forms gray, distorted rhombohedrons
of saddle-like shape to about 1 mm.
The distinctive thing is that starry microcrystals of pyrite form perfectly straight bands, some wide, some narrow, along the outside edges of the calcite rhombohedrons
, or following striations across their faces.
In the mid-eighties Caris returned to abstraction, leading to a completely new chapter of form vocabulary emerging from the mid-nineties, namely rhombohedrons
or polyhedrons of rhombuses.
Calcite crystallizes in a trigonal-hexagonal cell and typically forms scalenohedral (rhombohedrons
) crystals, aragonite has an orthorhombic cell with dipyramidal (needles) shaped crystals, and vaterite has a hexagonal cell with dihexagonal dipyramidal (discs) shaped crystals.
The etire lore of cones, cubes and cylinders, triangles and pyramids, parallelograms and rhombohedrons
had assumed mythic status in Western consciousness long before the introduction of coordinate analysis by Descartes in 1637.
The most typical crystals are milky white rhombohedrons
rimmed by a short hexagonal prism.
A similar approach has been helpful in identifying other calcite surfaces such as the (104) cleavage surface of control calcite rhombohedrons
and the (001) basal plane of calcite nucleated on glass (Sikes et al., 1994), as well as the (1-10) surface of calcite crystals that were stabilized by the presence of polyaspartate (Sikes and Wierzbicki, 1996).
For example, it's possible to build up a nonrepeating pattern in three dimensions simply by using two types of rhombohedrons
, which resemble skewed cubes.