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.
Hematite is the abundant form of iron oxide, natural red pigment, and an integral part of the largest iron ore deposits on Earth. Highly aesthetic crystals and shiny botryoidal hematite aggregates are also very popular collector specimens.