In addition, Madden & Hochella Junior (2005), studying the synthesis of hematite, observed that smaller particles had a plate-like morphology and the largest ones had the shape of both flat plates and rhombohedrons
His description is easy to follow, and he noted a place of special interest at Wasson Bluff: "Opposite the Two Islands, the fissures of the trap are lined with fine crystals of analcime and natrolite; and the fissures and vacant spaces of the trap conglomerate in the same neighbourhood contain a reddish variety of chabasie [chabasite] in rhombohedrons
, often of large size" (Dawson 1855, p.
Microsparite and sparite calcite crystals are mostly equant to elongated rhombohedrons
or scalenohedrons, but also a few prismatic crystals were observed.
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.
The most typical crystals are milky white rhombohedrons
rimmed by a short hexagonal prism.
All surfaces of these rhombohedrons
were observed by AFM to be the (1 0 4) cleavage surfaces and remained so after pyrolysis, which is understandable in that calcite is stable up to [tilde]825[degrees]C (Boynton, 1980; Dean, 1992), above which calcite decomposes to calcium oxide.
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.
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.
Those few which have been found are lusterless, elongated rhombohedrons
reaching at most 1 cm; they rest directly on chlorite or quartz and are rich in mordenite inclusions.
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.
In summer 2009, an unspecified mine in the Daye district began giving up calcite specimens showing gemmy, lustrous, butterscotch-orange crystals reaching 7 cm, some in loose groups and some on a dark gray, shaly matrix; the calcite crystals are flattened rhombohedrons
with secondary trigonal faces, and they are quite beautiful.
The Pallaflat mines (including the Southam pit and the Syke House pit) are famous for superb specimens of calcite in a variety of habits and combinations of rhombohedrons