Thursday, 4 June 2015

30 Days Wild | Day 4 - cataloguing my rock collection!

For day 4 of 30 Days Wild, I decided it was time to catch up on some geology admin! I'd had a few rocks lying around for a while, from various trips, that I hadn't yet got round to labelling and putting into my box'o'rocks (literally a shoebox with BOX'O'ROCKS written on the top). I like to label them all so I know where they came from, as if like me you are interested in geology, a rock can be a nice souvenir of somewhere you've visited. I've got some pretty exciting rocks in my box including lavas from Iceland, granite and gneiss from the French Alps and fossils from Dudley! The ones I labelled today were a piece of quartzite from the Stiperstones in Shropshire, some serpentinite and some gabbro from the Lizard peninsula in Cornwall, and a chunk of limestone from Winnats Pass in the Peak District, which was actually given to me by Alex from Sandwell Valley. I used the excellent BGS iGeology app to double-check the identifications of all the rocks!

Here they are all labelled up.
Rocks might seem a bit inert and removed from nature, but as the main component of the majority of soils is eroded rock, they influence ecosystems in a very profound way - just think of the unique flora of a limestone grassland. The serpentinite I collected in Cornwall is a great example - it is an ultramafic rock, meaning it is rich in magnesium and iron. This severely limits access to nutrients for plants growing in soils derived from serpentinite, leading to a very specialised plant community which is adapted to these conditions.

Because I think rocks are more interesting the closer you look, here are some macro shots taken with my field lens and smartphone camera!

Gabbro - a coarse-grained intrusive igneous rock, formed when magma slowly solidifies deep within the Earth's crust. Consists mainly of pyroxene, plagioclase feldspar and olivine.
Serpentinite - a very variable metamorphic rock, formed from peridotite which originates from the Earth's mantle; it has been uplifted to the surface and in the process been extensively altered.
More serpentinite - showing how variable it is!
Quartzite - a sedimentary rock (sandstone) consisting of well-cemented quartz grains. This rock looks dull and boring from a distance, but close to the quartz grains sparkle!
Limestone - a sedimentary rock formed in an ancient coral reef, mainly from fragments of calcite shells and skeletons of reef-dwelling animals - here you can see some crinoid stem plates.
This quartz has precipitated into a fissure in the limestone. Lovely stuff!

No comments:

Post a Comment