How rare is rare?

Mineral Matters #421

Ed Richard recently posed a question relating to rarity.

The question was “can we call a mineral 'rare' if it has been found only once, at one location but in reasonable quantity ( say between 100 - 200 good pieces)”.

Many interesting responses.

Now of course, the concept of rare can be applied to a much wider range of things.

One that I came across recently was a new mineral, jianmuite, formula ZrTi⁴⁺Ti³⁺₅Al₃O₁₆, reported from two locations. You can read the abstract here.

The first is a chromium orebody near Kangjinla, Tibet, China. Here it occurred as, wait for it, an inclusion in a corundum grain! Associated species included wenjiite, osbornite, and Strontium-rich dmisteinbergite.

The second locality is the Allende meteorite, the largest carbonaceous chondrite ever found on Earth. The fireball was witnessed at 01:05 on February 8, 1969, falling over the Mexican state of Chihuahua. Over 2 tonnes of material was recovered. The new mineral occurred as several grains with corundum, mullite, tistarite, and kaitianite, in the matrix of the meteorite. Several grains!

Now THAT is rare! 😆

Below: A slice from the 4.5-billion-year-old Allende meteorite.

Image by Shiny Things - originally posted to Flickr as AMNH - Meteorite, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=4196153.