Siderite is both an iron ore and gangue mineral. Its principal economic value lies in its high iron content and the absence of process contaminants such as sulfur or phosphorous. It is part of a large group of isomorphous minerals, the calcite group carbonates, which share similar physical properties, and rhombohedral crystal form.
Dioptase is a secondary copper silicate, occurring naturally as an oxidation product of hydrothermal copper deposits. It is renowned as a spectacularly colorful rival to emerald, but is too soft and too fragile to be cut as a gemstone, mainly because of its perfect cleavage.
The Klondike (Yukon) Gold Rush holds the record as one of the shortest-lived mining booms ever, lasting a scant 2 years, from August 1896 to September, 1898, when it was undermined by the slightly longer-lived Nome (Alaska) Gold Rush (September 1898 to 1905).
Aragonite is the less known cousin of calcite. Despite the lack of popularity, aragonite crystals and stalactites are among the most aesthetically-pleasing mineral specimes. Aragonite is present in various hydrothermal environments and it is the principal component of mollusk shells, coral skeletons and pearls.
Molybdenite is the principal ore mineral of molybdenum and rhenium. It occurs widely in igneous and metamorphic rocks generated under high temperature conditions. Despite its lack of popularity and rare crystal forms, it is a very interesting and important industrial mineral.
Crocoite is a rare lead and chromium secondary mineral. Its rarity, bright red color, and exceptional crystal forms have guaranteed its place as a prized collection mineral. Crocoite is the first historic source of chromium and natural yellow pigment - unfortunately highly toxic.