prehnite
/ˈpreɪnʌɪt/Mineralogy
noun
A mineral of the orthorhombic crystal system which consists of a hydrated silicate of calcium and aluminium, Ca2Al2Si3O10(OH)2, and occurs as pale green, yellowish, or colourless crystals in spherular aggregates, or as vitreous masses.
Origin
Late 18th century. From German Prehnit from the name of Colonel Hendrik Prehn, Dutch commandant at the Cape of Good Hope, who brought specimens of this mineral to Europe + German -it.