Crystal growth in pegmatite

The morphology of single crystals, the surface microtopographs of crystal 

Among eight Be-containing minerals in the BeO-Al Og-SiO -H O system, beryl has the widest stable range (=siOkbar, 320 —680 °C) [2], and exhibits a relatively stable Habitus bounded by 0001 and [1010] faces crystals showing spear-shaped tapered forms, or crystals containing channels parallel to the c-axis. 

At the final stage, F, the trapping of vapor-liquid two-phase inclusions is particularly remarkable a growth-dissolution-regrowth process of this t5q e is repeated six times, and this is routinely observed in beryl crystals from pegmatite localities 

At a later stage of volcanism, volatile components are supplied from the magma and crystals of sulfur or hematite crystallize around volcanic fumaroles or in fissures of surrounding rocks. Compared with crystallization in pegmatite, the environment is much more open, and the crystals of sulfur and hematite grow due to the chemical reaction occurring when the components supplied in the vapor phase oxidize at the Earth s surface. This crystallization therefore corresponds to 

Elemental growth spiral step patterns are observed on all (0001), 1011, and 1010 faces of hematite crystals grown by post-volcanic action. 

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In natural crystals, whose growth processes cannot be directly observed, the difference in R is recorded as the difference in separation in growth banding (see Chapter 6). Based on these observations, several papers were reported in which the direction of flow of ore-forming fluid was evaluated in pegmatite and hydrothermal veins. In many cases in which the natural mineral crystals exhibited extensively malformed Habitus from that predicted by the structural form, the malformation could be considered to be due to the remarkable anisotropy involved in the environmental conditions, such as the directional flow of the solution, which is similar to the situation of growth of NaCl from solution in between two glass plates, as discussed above. 

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