And unlike other
rocks, it does not consist of minerals.
Alison Christine via Flickr.com
Instead, it consists of
dead plant material that
has turned into rock.
It does, however, occasionally contain
minerals (that have accidentally entered it from other rocks - they
have not been formed in coal), such as calcite, dolomite, siderite,
marcasite, quartz, pyrite, sulfates and phosphates.
Jeffrey Beall via Flickr.com
This rock is brown or black in colour. It is fine grained.
interlayered with other sedimentary rocks.
It forms when layers of dead
plant material at tropical swamps are pushed deeper down by new layers.
Old coal mine by Ron Reiring via Flickr.com
Deep down they turn in to peat,
and later to rock under pressures from
the above layers, and at increasing temperatures.
Most coal formed in
the ideal conditions for its formation during Carboniferous
Kym Farnik via Flickr.com
It does not form at that pace now and coal is therefore not a renewable
If we overuse it, we will run out of it.
Burning coal also
releases CO2 into