SYLVITE
Sylvite is similar to halite in chemistry &
physical properties, but is scarcer. Sylvite is KCl - potassium
chloride. It has a nonmetallic luster and varies from clear to white to other
colors due to impurities - often red from hematite. Sylvite is soft
(H=2), water soluble, and has cubic cleavage. Sylvite rock (sylvitite) flows
under intense pressure from burial, as does rock salt (halitite). Sylvite
flows much more readily than does halite. Some shafts drilled through
sylvite are known to have been quickly closed shut by sylvite flow. The
quickest way to identify sylvite is by taste. It has a strong bitter
salty taste. Halite lacks the sharp bitter taste of sylvite.
Sylvite is an evaporite mineral - it forms by the
evaporation of seawater (along with halite, anhydrite, gypsum, and other
minerals). Sylvite has economic significance as the principal source of
potassium. The K is most frequently used as an ingredient in agricultural
fertilizers.
Sylvite
(red) mixed with halite (clearish gray) (field of view 2.6 cm across).