Ammolite, revisited…While I did cover this lovely gem material before (see on.fb.m
Ammolite, revisited…While I did cover this lovely gem material before (see http://on.fb.me/1H2oeQy), the advent of #cephalopodweek gave me an excuse to trot out these lovely photos I’d accumulated. It is often mislabelled as opal, or opalised ammonite, though gemmy silica with play of colour has nothing to do with it, and the sheen comes from a totally different mechanism. Ammolite is in fact fossilised mother of pearl, like you see in a mussel or nautilus shell (their remaining closest living relatives), and gives us an idea of how these creatures looked as they swam thorough the seas of the Mesozoic.Opals play of colour is due to regularly stacked and spaced silica spheres diffracting the wavelengths of light, while ammolite’s shifting red and green glows are due to thin film interference between rays of light reflecting from different layers in the stacked strata of aragonite crystals that form the nacreous shell. The same phenomenon it responsible for the sheen of oil or petrol on a puddle of water. Thicker layers of nacre produce the red to green hues and thinner ones blues to violet, reflecting which wavelengths of light they approximate to.LozImage credit: 1 Jewel Expert 2 Gregory Philips -- source link
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