Microline has the formulae KAlSi3O8 and a relative hardness of 7. It has the same composition as orthoclase but is distinguished by triclinic twinning (usually requires a microscope). If a felspar is a deep green it is microline – and sometimes called ‘amazon stone’ or amazonite after the Amazon river. It is recognisable from plagioclase by a lack of striations.
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