The wealth of material in amongst all these cobbles scattered along the Ormsaigbeg shoreline is quite amazing - easily enough to fill a university geology lab with specimens.
This one is a basalt lava probably dating from some 60 million years ago, the period of eruption when Ardnamurchan was a volcano. You would find similar specimens on the slopes of places like Hawaii, produced when red-hot rivers of lava cool. Its dark colour, and the spots of rust, show that it's rich in iron though, to pick it up, it very light in weight since it's full of bubbles created by escaping gasses.
In this specimen, the escaping gases formed bubbles which later filled with a white mineral precipitated from ground waters moving through the rock. These bubbles are called amygdales.
Some of the amygdales are quite large - the barnacle gives a sense of scale - and have been filled with crystals. There are crystals of two minerals here. Even larger amygdales are called geodes, and sometimes contain prettily coloured minerals such as amethyst and agate. They're often seen in curio shops and, we've been told, do occur around Kilchoan - but we haven't found any yet.
The wealth of material in amongst all these cobbles scattered along the Ormsaigbeg shoreline is quite amazing - easily enough to fill a university geology lab with specimens.
This one is a basalt lava probably dating from some 60 million years ago, the period of eruption when Ardnamurchan was a volcano. You would find similar specimens on the slopes of places like Hawaii, produced when red-hot rivers of lava cool. Its dark colour, and the spots of rust, show that it's rich in iron though, to pick it up, it very light in weight since it's full of bubbles created by escaping gasses.
In this specimen, the escaping gases formed bubbles which later filled with a white mineral precipitated from ground waters moving through the rock. These bubbles are called amygdales.
Some of the amygdales are quite large - the barnacle gives a sense of scale - and have been filled with crystals. There are crystals of two minerals here. Even larger amygdales are called geodes, and sometimes contain prettily coloured minerals such as amethyst and agate. They're often seen in curio shops and, we've been told, do occur around Kilchoan - but we haven't found any yet.
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