One woman's quest for geological understanding!

April 2014Monthly Archives

“Tuning fork” graptolites

graptolites final

This is a slab of slate with many specimens of the “tuning fork” graptolites, Didymograptus murchisoni.

Graptolites are very imported index fossils in the zoneation of the British Ordovician.
These are from the Llanvin Series, Abereiddy Bay, Dyfed, South Wales.

Baryte in Thin Section

This is a thin section of  radial growths of Baryte (or Heavy Spar).

This slide shows plumose (literally like feathers) interference structure.

In thin-section it is similar to other sulphates but can be distinguished by its straight extinction, moderately high relief, small 2V and paragenesis.

  • Crystals are often intergrown, rosettes, as demonstrated in this TS.
  • Four cleavage directions.
  • Interference colors rangeup to first-order yellow.
  • Sometimes pale colors-brown in PPL with weak pleochroism.

Collected from a mineral vein in the Hope Valley, near Castleton, Derbyshire.


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GEOLOGY OF WHITBY: Why do the East and West cliffs look different?

When you next take a stroll along the Pier at Whitby, stop at the light house, and look back towards the town. You will notice that the cliffs on either side of the pier look very different to each other. Why?


East Cliff

The East Cliffs have lots of horizontal layers of dark and light rock—shales and sandstones.

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Fossil of the week: “Horn Coral”

Heliophyllum (or “Horn Coral”) is an extinct Genus of Coral that existed predominantly in the
Devonian (408-360 million years ago).
This well preserved specimen was found in the beechwood limestone (Clark County, Indiana, USA)

This picture of the Heliophyllum horn coral shows the beaded pattern along its septa lines.

Heliophyllum (Rugosa / Horn Coral) Heliophyllum (Rugosa / Horn Coral)

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