• Locality: Koch Shaft, Silver Mines District, Madison County, Missouri

• ​Provenance: Ex. Cox Collection

• ​Primary Minerals: Wolframite, Zinnwaldite, Topaz, Quartz

• ​Rock Type: Greisen (Hydrothermally Altered Granite)

• ​Weight: 8 lbs 6.6 oz (3815 Grams)

• ​Dimensions: 7" x 4.5" x 3.75"

• ​Condition: Raw, natural field-collected state, unpolished

​Museum-Sized Provenance: The Cox Collection

Welcome to KeepsCache. We are proud to offer this museum-sized, 8.4-pound master reference specimen from the historic Koch Shaft in the Silver Mines District of Missouri. Formerly housed in the noted Cox Collection, this is an advanced, old-stock geological specimen that perfectly captures the violent magmatic-hydrothermal history of the St. Francois Mountains. Finding an intact, primary ore block of this sheer size and weight from this closed locality is incredibly rare.

​The Greisen Assemblage

This massive, unpolished cabinet block is a textbook example of a high-temperature "greisen"—formed when superheated, fluorine- and lithium-rich fluids cooked the native Precambrian granite.

• ​The Heavy Metal (Wolframite): The sheer density of this specimen is staggering. Hidden beneath the heavy, natural rust-red iron staining are massive, incredibly heavy deposits of Wolframite (Tungsten ore). This extreme specific gravity is the true hallmark of premium Koch Shaft ore.

• ​The Mica (Zinnwaldite): Distinct, dark, micaceous flaking is visible in the matrix pockets. This is Zinnwaldite, a rare lithium-iron mica intrinsically tied to these extreme high-temp vein systems.

• ​The High-Temp Silicates (Topaz & Quartz): Locking the heavy metals and micas together are large, structural chunks of glassy, hydrothermal quartz intergrown with high-hardness Topaz, punching through the heavy iron oxidation to provide a crystalline contrast.

​This is a massive, heavy-metal hydrothermal anchor piece. For the serious collector of midwestern mining history, localized St. Francois geology, or rare tungsten ores, this Cox Collection boulder is an ultimate centerpiece.

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