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The "Crystal Mountain" in Egypt
A subvolcanic vault, filled with crystals of a hydrothermal event
Norbert
Brügge, Germany
Dipl.-Geol.
Not all of
here used pictures are my property. I have copied them however in the interest
of the generality from the Internet and with the hope, that the owners have
for it understanding.
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 Barite crastals (BaSO4) and/or Calcite crystals (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.
At first glance, the crystals of calcite and quartz are very similar,
but a closer look reveals the differences.Quartz crystals have six sides,
mostly with a pyramid-shaped crystal tip.The crystals of Calcite, on
the other hand, can be rhombohedral (crystal with six rhombus-shaped
sides) or scalalenohedral (triangles with different lengths and with
different numbers of sides).
Every specialist
will confirm that they are not quartz crystals
what we see.
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
speleothems.
It is a subvolcanic vault, which was emerged probably during the Oligocene
age. The visible layers are limestones of the Khoman Fm.
(Late Cretaceous age), as well as included a coal seam and reddish to
brownish ferruginous layers above. The strata are broken or brecciated
and intensely with each other folded. It is to be ascertained intense
heat. The coal seam 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 grow in cavities.
It were also formed columns or domes with crystals within.
Occurense of Baryte
Mineralization in Bahariya Depression, Western Desert, Egypt
Y. S. Haroun &, M. F.
Raslan (2009)
"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 trend.
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."
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Travertine from Egypt's Western Desert: a terrestrial
record of North African paleohydrology and paleoclimate during the
late Pleistocene
Gloria Jiminez -- M.S., Earth and Planetary Sciences, University
of New Mexico, 2014
"The Crystal Mountain exhibits fluvial barrage and perched springline
facies, including pourover dams, microterracettes, and dissolution
caves. Much of the travertine at Crystal Mountain showed evidence
of recrystallization, with abundant sparite textures. We note
that the lack of vegetative facies at Crystal Mountain could suggest
high-temperature deposition, but further study would be required
to confirm this. Previous attempts to date travertine at Crystal
Mountain (Holzkamper, 2004) yielded ages out of U/Th range. We have
obtained the first date on Crystal Mountain travertine, of 523 �
30 ka on a groundwater speleothem-type structure, which is interpreted
to be the youngest carbonate in this deposit. Our date of 523 �
30 ka comes from the stratigraphically youngest unit we observed
at Crystal Mountain, and δ 234U model ages suggest greater deposition
earlier in the Pleistocene.
Finally, at Crystal Mountain, samples form two groups; one, with
groundwater speleothem-type samples, has similar δ13C values to
Kharga and Kurkur areas.The other group of Crystal Mountain samples
includes perched springline facies that may have been deposited
at high temperatures, and these have extremely depleted δ13C
values of -8 to -11�. Given the lack of vegetated textures in Crystal
Mountain travertine, as well as the possibility of hydrothermal
deposition at that site, it is doubtful that the isotopically light
d13C at Crystal Mountain originated from vegetation."
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My comment:
That are marine limestones and belongs to the Khoman formation,
it is not travertine. The age determination data at speleothems
are not applicable for the origin of the Crystal Mountain
(included the primary mineralization).
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