The "Crystal Mountain" in Egypt
A subvolcanic vault, filled with crystals of a hydrothermal event
It should once
be put right, that the crystals from the known Crystal Mountain (28°
26' E and 27° 39' N) between the oasis Bahariya and Farafra, northern
of the White Desert, are no Quartz crystals. They are probably Barite
(Schwerspat, BaSO4) and/or Calcite crystals (Kalkspat, CaCO3), which
to ascertain at the hardness of the crystals easily. Quartz (SiO2) has
the hardness 7, Barite and Calcite the hardness 3.5-3.0 (Mohs-scale).
Quartz crystal can scratch glass, Barite or Calcite can it not.
The origin of this Crystal Mountain is interesting. The hill was opened
during works at the road from Farafra to Bahariya by chance and destroyed
in part. The material was installed into the road. Today is the Crystal
Mountain a popular stop for the tourists.
Still more interesting is the geological context. The hill is
not a paleokarst cave with columnar-shaped stalagmites. It is a subvolcanic
vault, which was emerged probably during the Oligocene age. The visible
layers are e.g. White Desert limestone of the Khoman Fm.*
(Late Cretaceous age), as well as a younger coal seam and hydrothermal
impregnated reddish to brownish ferruginous layers. The strata are broken
or brecciated and intensely with each other folded. It is to be ascertained
intense heat. The coal seam e.g. was transformed to anthracite (?).
The crystals have increased out of climbed hydrovolcanic solutions.
The hot solutions were high concentrated with BaSO4 and/or CaCO3, which
had been solved from the sediments. The solutions have penetrated into
all cavities. After cooling of the solutions the crystals could increase.
It were formed columns or round domes with crystals within.
The white limestone of the Khoman Formation is dated
as middle to latest middle Maastrichtian (Gansserina gansseri and Contusotruncana
contusa foraminiferal Zones). An open marine, warm Tethyan outer shelf
environment of deposition is inferred.
"High grade Barite mineralization
is found mainly in the form of different veins restricted to the ground
surface of Bahariya depression. The barite veins trend in different
directions and are actually associated with the major folds and faults
that are restricted to the oldest rocks of Sabaya Formation which form
the floor of the depression. The latter occurs within a major northeast
trending belt of considerable extension about 100 km long and 40 km
wide. Several other folds of the same or later tectonic phase but of
lesser extension occur parallel to or perpendicular to the main anticlinal
The Barite veins are widely distributed to the south of Gebel El Hafhuf
which is composed of a rock sequence including sandstone, shale, limestone,
phosphatic limestone and phosphatic calcareous sandstone. This succession
is capped by the Oligo-Miocene basaltic sheet which takes the form of
open circle of about 20 m thickness.
The barite veins are restricted to the fractures that are parallel to
the main E-W or NW-SE striking faults in the Sabaya Formation. These
veins occur subparallel sets with more than 7 m length and ranging in
width between 0.5 to 4 m. These veins are numerous and distributed in
association with tectonically formed fractures and fissures.
Barium was leached from the basaltic extrusion during high temperature
circulation. Tertiary Oligocene basalt at Gebel El Hafhuf, Bahariya
Oasis is related to continental intraplate volcanism. Fumarolic and
geyser activities belong to Oligocene period were consider as gas maar
resulting from a phreatic explosion.
Release of sulphate fluids from the sulphate-rich minerals involved
in the Brine deposits distributed within Bahariya Depression at the
Quaternary, namely polyhalite, kieserite and kyanite.
Migration of these fluids through the deformed strata followed by barite
mineralization as a result of a rapid primary precipitation at or above
the sediment / fluid interfaces.
The crystals are transparent to translucent and are generally present
in the form of angular to subangular shape."