PLACER
GOLD CRYSTAL
Gold nuggets found in rivers & streams (= placer
gold) usually have irregular, somewhat rounded shapes. It's rare to find
placer gold having a crystalline structure. HereŐs the top and
bottom of a nice gold crystal from VenezuelaŐs Santa Elena Placer Gold
District.
The top of the specimen (left photo) shows the upper
half of an octahedral crystal (a square pyramid). Notice that each of the
four faces of the pyramid are embayed. Such features are not uncommon in
natural crystals. The terms hopper octahedron or skeletal
octahedron would be applicable here. A few grains of sediment are
stuck at the bottom of a couple of these cavities (e.g., just visible in the
bottom cavity of the left photo). The right photo shows the underside of
the specimen. It has the typical irregular, dimpled, somewhat rounded
shape of many placer gold nuggets.
Geologic context: placer gold in modern alluvial deposit; gold is
derived from weathering of conglomeratic paleoplacers in the UairŽn Formation,
Roraima Supergroup, upper Paleoproterozoic, ~1.7-1.8 billion years.
Locality:
unrecorded locality in the Santa Elena Placer Gold District, near Santa Elena
de UairŽn, Grand Savannah River region (La Gran Sabana), southeastern Bolivar
State, southwestern Guyana Highlands, southeastern Venezuela.
Crystalline placer gold (skeletal octahedral crystal; hopper octahedral
crystal) (5.5 mm across) from the Santa Elena Placer Gold District of
Venezuela.