Geo Advent Calendar Day 25

O Christmas tree
O Christmas tree
How lovely are thy minerals!

Sadly we’ve reached the end of the Geo Advent Calendar… but that means it’s Christmas! The best way to celebrate Christmas is with a mineral tree. The baubles have pictures of thin sections on them and were made by Ruth Siddall. You can download them here.

Merry Christmas everyone! (more…)

Geo Advent Calendar Day 24

These lovely dendrites grew along a limestone bedding plane. The growth of dendrites is similar to snowflake formation; when a material is below its crystallisation temperature, fractal branches form instead of crystal faces. Dendrites are also a pseudofossil as they can be mistaken for fossil plants. (more…)

Geo Advent Calendar Day 23

‘Twas the #FossilFriday before Christmas
When all through the house
Not a creature was stirring
Not even a bivalve

With a coating of tiny pyrite crystals, this bivalve is perfect for the festive season! (more…)

Geo Advent Calendar Day 22

Did you know a geologist’s favourite dog is a labradorite? This mineral is a feldspar and is named after the Labrador region in Canada – this is where the type specimen comes from. Labradorite is well-known for its optical effect called labradorescence, a vibrant colour display caused by its crystal structure.

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Geo Advent Calendar Day 21

When ammonite fossils are replaced by pryite, it can give them a Christmassy appearance. Pyrite replacement occurs in reducing, marine environments. When an organism decays, sulphide is released and reacts with dissolved iron in water to produce pyrite. This webpage gives a nice overview of how mineral replacement occurs. (more…)