This is my second contribution to the current Alphabetical Series in the Facebook Group “New Zealand Lapidary, Rocks, Minerals, Fossils”. In the 2021 version of this Series I posted “B is for Botryoidal Chalcedony”. My first 2025 entry was “A is for Agatised Fossil Bone”.
“B is for Banded Argillite”
I found this stone on Gemstone Beach, Southland, in September 2024 – see the end of the Post “Sunday 8 September 2024: Fifteen Finds from a First Gemstone Beach Fossick”. It is a handful, nine centimetres wide. Argillite is a sedimentary rock that sometimes shows a banding, reflecting layers of different coloured sediments. On Gemstone Beach, banded argillites can be found in hues of green, grey, black and brown. Sometimes I think that this particular stone is brown, sometimes I wonder if it is grey – colour perception is subjective. Many of Gemstone Beach’s banded argillites appear to have been subject to more heat during formation than other argillites, their bands looking as if they melt into each other, like pottery glaze. They tumble polish well. This one is too big for me to tumble polish – it sits outside in the garden at my home in Whanganui and looks brilliant after rain.
For more details about Gemstone Beach’s banded argillites, see Stones Gn8 to Gn14 in “Gemstone Beach and its Stones: An Introduction for the Passing Motorist – Part Seven-A, Green Argillite Stones”.
The next entry is “C is for Calcite (Calcium Carbonate) in a Ward Beach Fossil Oyster Stone”. An Index for this Alphabetical Series is here.
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