Geoscience Reference
In-Depth Information
271
Figure
271
shows the microscopical appearance of an
unhydrated FGD gypsum plaster. The colour of the plaster
in hand specimen is white as it consists almost entirely of
fine hemihydrate particles and is without the iron-rich
impurities of natural source gypsum. Figures
272
and
273
show the appearance of hydrated FGD gypsum plaster from
the same source, chiefly comprising of a mass of small,
interlocking crystals of gypsum. Traces of limestone and
quartz particle impurities are seen in Figure
272
and Figure
273
illustrates growth of larger gypsum crystals in a void.
A
GGREGATES AND ADDITIVES
Low-density aggregates, such as perlite (
274
) and
vermiculite (
275
), are important ingredients in modern
271
Unhydrated FGD gypsum plaster consisting
almost entirely of hemihydrate particles (grey/yellow);
XPT, ×35.
272
273
272
Close view of hydrated FGD gypsum plaster
comprising a mass of gypsum crystals (grey) with rare
impurities (centre) consisting of limestone (light
brown) and quartz (grey) particles; XPT, ×150.
273
Close view of hydrated FGD gypsum particles
showing interlocking crystals of gypsum (white) and
air voids. Larger laths of gypsum line the void to the
right of centre; PPT, ×300.
274
275
274
Perlite lightweight aggregate (white) in a
premixed lightweight gypsum plaster. The expanded
perlite particles comprise clusters of hollow bubbles
with walls of volcanic glass; PPT, ×35.
275
Exfoliated vermiculite lightweight aggregate (grey)
in a premixed gypsum plaster (grey), comprising
concertina-shaped granules of vermiculite flakes; PPT,
×35.
