Civil Engineering Reference
In-Depth Information
7
Stone
Many myths compare stones with the bones of Mother Earth. Extraction of min-
erals in most cultures has been accompanied by complex rituals and rites, under-
taken as carefully as possible by, amongst other things, filling up the holes and
passages into the mine when the extraction was finished. A Sioux Indian small-
holder expressed this spiritual attitude thus:
'You ask me to dig in the earth. Do I have to take a knife and plunge it
into my Mother's breast? You say that I must dig and take away the
stones. Do I have to remove her flesh to reach down to her bones?'
There are three main categories of stone:
•
Igneous stones
. Consolidated pieces of rock which have forced their way up
through splits in the crust of the earth. These are the hardest types of rock such
as the granites, syenites and dolerites.
•
Sedimentary stones
. Petrified and disintegrated stone which has combined with
organic materials. In this group are sandstone, slate and limestone.
•
Metamorphic stones
. Formed by exertion of pressure and the action of high tem-
peratures on igneous or sedimentary rock types, which transforms them into
another structure. Examples of these rock-types are crystalline slate and
quartzite.
None of these groups can be referred to as the oldest, as the geological processes
are in a continuous, rotational process. Sedimentary rock types can be formed
through hardening of gravel, sand and clay which originate from the disintegra-
tion or breaking down of igneous or metamorphic stones; igneous stones can
arise through the smelting of metamorphic and other types of rock and a later
consolidation, and metamorphic stones can arise from changes in older sedi-
mentary, igneous or metamorphic stones.
