"الجيولوجيا والموارد المعدنية في كلٍ من محافظة ظفار ومسقط وعُمان" [ظ‎‎٣‎٨] (٩٦/٦٦)

50
%
Gypsum and Anhydrite
84. Although fragments of Gypsum are to be found on, and as
veins in, the limestones and sandstones and slates at the head of the
Ghaiz wadi, towards the Ansarit gap where the vertical veins of
fibrous Gypsum are 6 to 8 inches wide, there is no_ considerable
deposit which could be worked on a commercial basis for export.
Gypsum, with perhaps some Anhydrite, is more common across the
Jabal Qara in the Qarn Shaiba country, but it is again present,
so far as my observations went, only as irregular veins and segrega
tions in the limestone. I had thought, after discovering the ‘chalk’
beds not to be chalk, that what has since been proved to be pure
Dolomite was massive granular Gypsum (or perhaps Anhydrite).
There is so much evidence of Gypsum in that northern area that
extensive deposits might be discovered, though it might be difficult
to account for the sources of the Sulphuric acid which has reacted
to form the Calcium sulphate. In the case of the wadi Ghaiz
veins the probability is that Pyrite was present and the decom
position of this Iron sulphide would yield the necessary Sulphuric
acid to react with the limestone or water-carrying Calcium carbonate
in solution to form Calcium sulphate [as Gypsum in its various forms
—satin spar (fibrous), selenite (crystals), alabaster (fine grained), etc.].
Dark, pyritiferous shales occur with many lignitic coal seams and
with carbonaceous shales among bedded limestones, and these
might quite easily yield the necessary Sulphuric acid for the formation
of Gypsum and become themselves so leached as to be found now
as beds of ‘Multani matti’ or ‘fuller’s earth’ and the like. I noticed
no such beds in Dhufar, but my traverses were such that any
exhaustive search was impossible, and such clays would not be very
conspicuous in scarp and cliff sections. It does not follow that,
because I found no massive bed or deposit of Gypsum, none exists.
Indeed, I believed the ‘chalky bed’ to be Gypsum and I was rather
surprised to find it was Dolomite (the chemical formation of Dolomite
from coral or foraminiferal limestone requires percolating water
charged with Magnesium chloride or at least much Magnesium salt in
the presence of Sodium chloride). It is quite likely that beds of
Gypsum will be found towards the Nejd.
Hematite (Iron Ore)
85. A fragment of specular Hematite was handed to me by
Mr. Mohammad Amin Salim, who stated that it was reported to
have been found in the Murbat area. I was unable to secure further
specimens or any reliable information as to the source of the specular
mentions ‘micaceous Hematite’, used as kohl
(s y^nite) mistakenly by the Bedouin of Makalla, from several places
in hat country, but his various specimens proved much of it to be