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silicate-carbonate material (from 1 to 20 vol%) that is either present interstitially among
halite crystals or forms irregular compact masses veined by chlorides. Contacts between
silicate-carbonate material and chlorides are decorated by euhedral grains of olivine,
monticellite, djerfisherite, perovskite, pyrrhotite, shortite and magnetite.
a
b
d
e
c
Fig. 10. Occurrence of chloride nodules in kimberlite (a, b) and textural characteristics and
mineral relationships in the chloride-carbonate nodules (c-e). c, d—sample UV-5a-03 show
texture resembling liquid immiscibility; white zoned sheets are composed of carbonates
(Na-Ca±K±S), greyish masses cementing sheets are chlorides (halite-sylvite). e—sample
UV-2-03, composed of shortite, northupite and chlorides. Scale: 1 graticule=1 mm
Chloride-carbonate nodules contain roughly similar amounts of chloride and carbonate
minerals that are regularly interspersed (Fig. 10 c-e). Carbonates are present as 1-5 mm thick
sheets with a bumpy or boudin-like surface. The groups of aligned, subparallel sheets make
up rhombohedron formations (2-2.5 cm) that resemble hollow (skeletal) carbonate crystals
(~78 o angle) in shape. Cross-sections of inflated parts of the sheets show symmetrical zoning
that reflects the change from translucent to milky-white carbonate (Fig. 10 c, d). The intra-
sheet space and cracks in carbonate sheets are filled with sugary aggregates of chloride
minerals. A texturally and mineralogically different variety of the chloride-carbonate
nodules is represented by a single sample UV-2-03 (Fig. 10e). In this ~15 cm nodule,
carbonates are present as very thin (< 0.2 mm) aligned white calcite-shortite sheets, as well
as individual well-formed yellowish crystals of shortite and northupite (up to 1 cm). In the
carbonate intergrowths northupite is interstitial and less abundant (25-30%), and can be
distinguished from shortite by crystallographic properties and higher transparency.
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