Closer examination of the cement with SEM and in thin sections indicates that it is composed of micritic ([less than or equal to] 4 [micro]m), microsparitic (4-10 [micro]m) and sparitic (from 10 to 200 [micro]m) angular equant to elongated rhombohedral and scalenohedral
or prismatic calcite crystals (Figs 6, 7).
Carbonated CaO particles resembled typical scalenohedral
calcite crystals, while carbonated MgO particles resembled typical platy hydromagnesite crystals (Figure 6).
PCC pigments of calcite and aragonite crystalline polymorphs having rhombo-hedral, orthorhombic, and scalenohedral
habits were selected for the study.
Siemroth (1990) writes that scalenohedral
calcite crystals to 10 cm long were found on the old mine dumps at some time or times after mining ended in 1922.
For instance, in ordinary mineral water, residual particles are scalenohedral
(shapeless); most of them adsorb organic and biological elements and compound polydisperse environment with particles from 3 nm to 100 m[micro] and larger ones.
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.
As filler for internal loading to paper, the spherical hollow particles maintained sheet density of handsheets with only minimal density reduction, and effectively increased specific light scattering coefficient (probably because of their porous structure.) This optical effect was higher than for conventional ground calcium carbonate, but lower than for commercial coagulated scalenohedral
particles with a large surface area.
A common mineral, early-stage calcite is found as pale brown to yellow scalenohedral
crystals which are translucent to opaque, commonly with black inclusions and colored surface coatings.
Some coated SBS producers are looking at the bulking benefits of 5%-8% scalenohedral
precipitated calcium carbonate (PCC) as a key to achieving brightness and smoothness without significant bulk loss.
This fissure, which extended for about 1.6 km, was lined with hexagonal prismatic calcite crystals toward one end and sharp scalenohedral
calcites towards the other, all colored red from included hematite.
The synthesis of a PCC scalenohedral
or rhombohedral filler could be controlled to increase the amount of internal voids in the range of 1-0.01 [micro]m in order to achieve higher light-scattering capacity.
Crystals are typically scalenohedral
, in radiating clusters.