c Study Mount Elephant‎ > ‎Geology‎ > ‎rock samples‎ > ‎

Basalt forms

(update 10/12/16)
The lava takes on different forms depending on what happens as it erupts. Here are some examples.

Under Mount Elephant is a layer of wet limestone. The molten lava mixes with steam and is ejected as frothy lumps which solidify before landing as scoria or "cinder".















 
The scoria takes different forms, depending on temperature and viscosity when ejected.

















Conditions must change fast. Here we have foamy lava lying (over/under/beside?) dense lava.

















Some lava can be very dense. 2 pieces hit together can ring like a bell.
This sample also has the blue iridescence.
















Some samples show where the cooling surface has been bombarded with falling rocks both foamy and dense.



















Some just flws out with no gas or steam involved.
The early eruption was all scoria and the last to erupt (on the surface in the crater) is solid with no holes.
















There are some strange forms. This is quite soft, with white spots at all the corners.


















The lava which is flowing as it cools can show the marks.
One section of the mountain 20m cubic has an iridescent blue colour.
Maybe from a hotter temperature or a particular mineral?
















Very glassy texture. 2 samples only.


















Some areas have both red and black lava together. Samples may be vescicular or dense. Maybe due to different proportions of iron?






































There are "volcanic bombs" ranging in size from 1cm to 1m in diameter.
They often have a solid basalt spindle shaped case, with a centre of green olivine crystals. They may be solid lumps of basalt of a particular temperature (about 1000 deg C) when ejected but spinning formed the shape and the olivine crystallized as they cooled.
Comments