Crystals equant

It is imperative to clearly distinguish the term polymorphism from the term morphology. Polymorphism refers to the crystal structure, while morphology describes the macroscopic shape of a crystal (equant (cube), lath, needle, flake, colum, and plate) [9]. The same polymorph can be easily crystallized in different morphologies however, different polymorphs can also have the same morphology. In other words, polymorphism and morphology are independent of each other. 

Over the past several decades six different silicate minerals have been mined as asbestos and processed for industrial and commercial applications. The most commonly encountered asbestos mineral today is chrysotile. The five other minerals are tremolite, actinolite, anthophyllite, grunerite, and rie-beckite. All five are members of the amphibole group of minerals, and each can occur as chunky, acicular, or equant crystals, as well as in fibrous form. When found as fine fibrous aggregates, in quantities appropriate for mining, they are usually distinguished as a special variety—for example, tremolite-asbestos. 

Prismatic A term commonly used in descriptions of minerals for crystals exhibiting aspect ratios usually below 3 and grading into equant (aspect ratio = 1). The term may refer to crystals embedded in a matrix, but is more commonly used to describe free-standing, euhedral crystals, whether micro- or macroscopic. 

Particle morphology refers to the external features or form of a powder s primary particles. This includes descriptions of shape, including aspect ratio, or crystal habit (plate, needle, lath, equant, etc.). Particles are not always observed as discrete entities. Rather, they are often associated with other particles, sometimes loosely held... 

Equant, blocky, prismatic (large crystal faces)... 

Rapid accumulation of silt and clay on mammillary surfaces stops crystal growth. Large numbers of very small, equant to columnar crystals that grade quickly to a few large columnar crystals (Fig. 6) mark the reinitiation of crystal growth. 

Figure 9. Scanning electron micrograph of the underside of a calcite raft that precipitated at the water-air interface in Browns Room. Perimeter has long crystals, whereas the central part of the raft is characterized by mostly equant crystals. Four small rafts coalesced to form this large one. Scale bar is 1 mm.

The final Devils Hole speleothem type is flowstone (Hill and Forti, 1997, p. 70-72), which precipitated from films of calcite-supersaturated water flowing down the exposed walls of Browns Room. Flowstone deposits in Browns Room characteristically are banded in cross section, with bands from about 0.1 to 3 mm thick (Fig. 15, 17). Each band is a depositional unit, with major or minor discontinuities on either side. Outer surfaces of bands commonly are etched and corroded, and may have thin coatings of clay-sized material. The inner, older bases of the bands are composed of large numbers of micron- and decami-cron-sized equant calcite crystals. The equant crystals rapidly grade into fewer elongate, length-fast calcite... 

Equant/cubic Crystal with similar length, width, and thickness... 

The crystals of a given substance may vary in size, the relative development of the given faces and the number and kind of the faces (or forms) present that is, they may have different crystal habits. The habit describes the overall shape of the crystal in rather general terms and includes, for example, acicular (needle-like), prismatic, pyramidal, tabular, equant, columnar and lamellar types. Figure 1.7 shows the crystal habits of a hexagonal crystal. 

Cement crystals are commonly bladed, equant or syntaxial in shape. Syn-taxial overgrowths are precipitated in optical continuity with the substrate... 

There are phlegmatized lead azides which in the physical appearance is entirely different from tlie aggregates which are typical of most processes. Instead of being opaque granules, they are equant transparent crystals (Figure 10). The first of these, called Service lead azide, is made by the near-simultaneous... 

The severe acid treatments separated the aggregates into single crystals in a size range of 0.5-10/un with an average mean diameter of 3/xm. Twenty per cent of the crystals are euhedral acicular and the remainder are equant and anhedral. 

The particular shape of crystals as determined by the relative growth of their faces is called the crystal habit. Long thin crystals are called acicular (needle-like), whereas tabular crystals develop most rapidly in two dimensions. Equant crystals, on the other hand, develop pretty much equally in three directions. Figure 104 shows a schematic classification of these descriptions of habit. Of course, some crystals exist in easily recognized forms, such as the ones described in the previous section—cubic, octahedral, tetrahedral, etc. 

Ciyptociystalline, equant high-Mg calcite First, ciyptocrystaUine second, acicular aragonite Similar to previous, but lengths of acicular crystals may be more than 30 fim. Crystals extend to center of pores... 

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