Rhodochrosite & Pyrite (China) *INTERESTING LITTLE SPECIMEN* for Sale

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Rhodochrosite & Pyrite (China) INTERESTING LITTLE SPECIMEN For Sale

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Rhodochrosite & Pyrite (China) INTERESTING LITTLE SPECIMEN:
$32.28

Little specimen of pink rhodochrosite with a well defined cubic crystal of pale brass-yellow pyrite on one face. From the Wutong Mine, Liubao, Cangwu County, Wúzhōu (formerly Ngchow), Guangxi Zhuang Autonomous Region, China, it approximately measures 20x15x7 mm and weighs 2.63 g.

Please note: this particular item is very small and is classed as a thumbnail-sized specimen (1-3 cm).

The Wutong Mine deposit was discovered in 1958 and was a minor producer of lead (4,676 tons), zinc (3,555 tons), and silver (6.65 tons). It went on a ‘care and maintenance’ condition in the summer of 2011. Ores are found in fractures (ladder type vein) in Cambrian chert, sandstones, siltstones and shales. There were three periods of faulting and mineral deposition, a pre-ore faulting, fracturing with deposition of quartz and hübnerite and a final faulting with emplacement of base metals, fluorite and rhodochrosite followed by sparse deposition of silver minerals. The temperatures of deposition started below 200°C, maxed above 300°C and then fell to below 100°C.

Rhodochrosite (a carbonate) is a manganese mineral that occurs in both aggregate and crystal form. It belongs to the wider Calcite Group of minerals, a group of related carbonates that are isomorphous with one another. In its (rare) pure form when the mineral has minimal iron content, it is typically a rose-red colour, but impure specimens can be shades of pink to pale brown. Transparent or translucent and with a vitreous or pearly lustre, colours may range from pink, rose, red, yellowish-grey, brown, white, grey; colourless to pale rose in transmitted light. When Rhodochrosite is exposed to the atmosphere, it may develop a thin film of manganese oxide on its surface. This may slightly darken the colour of a specimen. Rhodochrosite sometimes alters into black manganese oxides (such as pyrolusite, manganite, and psilomelane), and black manganese oxide stains are usually associated with rhodochrosite. The transparent raspberry-coloured crystal form is bought at high prices by collectors due to its rarity. Rhodochrosite also makes an interesting gemstone due to its distinctive raspberry red and pink stripes, but its main use is an ore of manganese, which is a key component of low-cost stainless steel formulations and certain aluminium alloys. Due to its composition, it is also referred to as manganese spar, or as raspberry spar with reference to its colour. Named in 1813 by Johann Friedrich Ludwig Hausmann from the Greek ρόδο, rose, and χρώς, colouring, referring to its colour, it is the national gemstone of Argentina and the US state mineral of Colorado (due to significant deposits being discovered in both places). Mohs hardness varies between 3.5 and 4.

Pyrite (a sulphide), or iron pyrite, is a very common mineral found in a wide variety of geological formations from sedimentary deposits to hydrothermal veins and as a constituent of metamorphic rocks. An iron sulphide, it’s considered the most common of the sulphide minerals. Pyrite can form in extremely well-crystallised examples of cubes, pyritohedrons, and octahedrons. Combinations of these forms also occur. An icosahedron formed from a combination of an octahedron and pyritohedron is also known. Pyrite crystals frequently form penetration twinning (crystal inter-growths), especially in the cubic form. Cubes are sometimes elongated in rectangular form. Also occurs massive, radiating, grainy, flaky, drusy, mammillary, encrusting, nodular, tuberose, fibrous, in concretions, and as groups of small crystals. Pyrite crystals are frequently striated, exhibiting tiny parallel line growths or grooves on the crystal faces. The metallic lustre and pale brass-yellow hues of pyrite has in many cases led to people mistaking it for gold, hence the common nickname 'fool's gold'. However, pyrite is quite easy to distinguish from gold: pyrite is much lighter, but harder than gold and cannot be scratched with a fingernail or pocket knife. Pyrite will slowly oxidise in a moist environment and release sulphuric acid that is formed during the process. However, whilst pyrite formed as sedimentary concretions has a tendency to decompose quickly, well-crystallised specimens are generally relatively stable. Mohs hardness 6-6.5.