Millerite is a nickel sulfide named in 1845 in honor of the English mineralogist, Professor William Hallowes Miller, University of Cambridge, who first studied the crystals. It commonly forms trigonal, metallic, tufts, radiating clusters, and spherules of acicular crystals which are pale brass-yellow to green-gray with an iridescent tarnish; also massive, cleavable. It is found in Cu-Ni sulfide deposits, sometimes in abundance. Millerite occurs in low-temperature deposits in carbonates, hematite, and serpentines. It is also present in geodes within limestone in Wisconsin, Illinois, Iowa, and Missouri, USA. Millerite is found in cavities of siderite at the type locality: Jachymov, Jachymov district, Krusne Hory Mountains (Erzgebirge), Bohemia, Czech Republic. In the USA, it occurs as spectacular, radiating clusters of brass-yellow, acicular crystals at the Sterling mine, Antwerp, Jefferson Co., New York; the Meikle mine, Bootstrap district, Elko Co., Nevada; and the Gap mine, Gap, Lancaster Co., Pennsylvania. Locations within Germany include: the Victoria mine, Littfeld, Siegerland, North Rhine-Westphalia, Germany; Friedrich Mine, Schonstein, Wissen, Siegerland, Rhineland-Palatinate, Germany; Willibald mine, Ramsbeck, Meschede, Sauerland, North Rhine-Westphalia, Germany. Other notable localities include: Thompson mine, Thompson Nickel Belt, Manitoba, Canada; Perseverance mine, Leinster, Leonora Shire, Western Australia, Australia; Ca' dei Ladri (Silla), Gaggio Montano, Bologna Province, Emilia-Romagna, Italy.
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