Putnisite, Earth’s Unique New Mineral Discovered

In the newest release of the Mineralogical Magazine (v.78) a study was published that indicates the discovery of the new mineral, putnisite. It’s named after Christine and Andrew Putnis who together are established contributors to the study of mineralogy.

Dr. Peter Elliott of South Australian Museum and the University of Adelaide led the team of research scientists. Dr. Elliott continues to add to his résumé, as this was just one of twelve other minerals he has discovered in Australia within the last few years. The team was sent to study the material after a prospecting mining company initially discovered it. The new mineral was found at a surface outcrop at Lake Cowan, in Australia.

Crystals of putnisite ( in purple). © Peter Elliott

Crystals of putnisite ( in purple). © Peter Elliott

What makes this mineral so special is its composition. Compared to the 4,000 other known minerals, putnisite is unique because it is composed of an interesting array of elements: strontium, calcium, chromium, sulfur, carbon, oxygen and hydrogen. The molecular formula is pretty complex: SrCa4Cr8(CO3)8SO4(OH)16•25H2O

The mineral is a translucent vivid purple with a pink streak. It is composed of brittle pseudocubic crystalline structures with a maximum size of 0.5 mm each. Dr. Elliot states in the Mineralogical Magazine, “By x-raying a single crystal of mineral you are able to determine its crystal structure and this, in conjunction with chemical analysis, tells you everything you need to know about the mineral”. He continues, “Most minerals belong to a family or small group of related minerals, or if they aren’t related to other minerals they often are to a synthetic compound – butputnisite iscompletely unique and unrelated to anything”.

It has a Mohs hardness score of 1.5–2 (the scale is from 1-10). In comparison, a human fingernail has a hardness of 2.2. The bonds between atoms within the crystal structure determine the hardness of a mineral. This means that putnisite lays between talc (the softest mineral) and gypsum (the second softest) when it comes to its texture. Diamonds score a 10 on Mohs’ scale, as they are the hardest known minerals.

It is still not yet known if there are any practical uses for the new mineral. Other soft minerals are used in a variety of bath and baby powders, also in sandpaper. Graphite has a hardness of 1.5 and is used in pencils. As a side note, putnisite and ice share the same Mohs’ scale hardness, ice is in fact technically a mineral. Being a soft material it is susceptible to weathering and breakage.

Sources and further reading:



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