Article Nº 0249 Geology and mineralogy Vol. I · p. 144
Aragonite
Aragonite, a calcium carbonate mineral found on basalts in Madeira and Porto Santo in several crystal forms.
Calcium carbonate; orthorhombic system. It occurs on the basalts of Madeira and Porto Santo (‘holy harbour’). On Madeira it is found in several forms: in geodes; in transparent twinned crystals resembling hexagonal prisms, but with re-entrant angles between the prism faces; in groups of needle-shaped crystals (acicular form), etc.
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