Ekanite – a mineral that will amorphise itself

What does it look like?

The crystal structure of Ekanite. The green atoms are the thorium which supply the radioactivity that breaks down the crystal structure over time. Image generated by the VESTA (Visualisation for Electronic and STructual analysis) software http://jp-minerals.org/vesta/en/

What is it?

Ekanite is a very rare gem, found originally in Sri Lanka, that is a olive green/brown colour. Not only is it quite a rare gem, but it also does something very unusual – it destroys it’s own crystal structure. This is because ekanite contains thorium, an element that often has high levels of radioactivity. The energy from this is enough to break down the crystal structure, and turn the material into an amorphous material, a glass where the atoms are arranged with little long range order. This phenomenon is known as metamictization, and does actually occur in another mineral we’ve featured – Zircon – when the inclusions of thorium are high enough.

Where did the structure come from?

The crystal structure of ekanite is #9004161 in the Crystallographic Open Database

Common structure, but rare material – Iridium Oxide

What does it look like?

Iridium Oxide, a rutile-type structure. Here the yellow atoms are Iridium and the red oxygen. Image generated by the VESTA (Visualisation for Electronic and STructual Analysis) software http://jp-minerals.org/vesta/en/

What is it?

Yesterday we introduced the Rutile structure, and today we thought we’d show case quite a rare material that takes up this structure, Iridium Oxide.

Iridium, like rhodium, is one of the least abundant elements in the crust of the Earth. Part of the reason for this may be that Iridium mixes well with Iron, it is a Siderophile element. Because of this much of the Iridium on Earth is through to have, along with much of the planets iron, dragged into the core.

In fact, the lack of iridium in the crust of the earth has made for a useful way of tracking how many meteorites have hit the earth in geological time. Because many types of meteorites are much more abundant in this element, finding areas with a little more iridium in the rocks suggests some extra-terrestrial interference. Iridium abundance was the basis for the hypothesis that a large impact from space wiped out the dinosaurs.

The lack of iridium on earth is a shame, as it is a very useful metal – the least corrosive of all the elements. In fact getting it to react at all is very difficult, but it can be forced to form irdium oxide from its powdered form. As such iridium oxide has been seen to display some exotic electrical behaviour.

Where did the structure come from?

This crystal structure was taken from a paper that described a number of rutile-type metal dioxide structures. It is #2101854 in the Crystallography Open Database.

A formally very exclusive mineral – Painite

What does it look like?

The crystal structure of Painite. Here the calcium atoms are purple, aluminum are light blue, green for zircon and dark green for boron with the red atoms representing oxygen. Image generated by the VESTA (Visualisation for Electronic and STructual Analysis) software http://jp-minerals.org/vesta/en/

What is it?

Painite, name after British mineralogist Arthur Pain, was once considered to be the rarest minerals in the world. It’s a borate (BO₃) mineral and when first identified only 25 specimens of this deep red minerals were known about – all from Myanmar. Of these, only two were faceted gems, which had a beautiful deep red colour (which is from the small amount of the elements vanadium and chromium that substitute into the crystal structure). However, in 2002, a new source of tis mineral was found, with nearly a thousand fragments of the mineral discovered.

Where did the structure come from?

The structure of Painite we’ve featured here was revealed by Moore and Araki, in 1976, from a specimen kept in the British Museum.

An exclusive mineral – Bowieite

What does it look like?

The crystal structure of Bowieite, the rhodium atoms are grey and sulfur atoms are yellow. Image generated by the VESTA (Visualisation for Electronic and STructual Analysis) software http://jp-minerals.org/vesta/en/

What is it?

After gold, Rhodium is the most expensive metal. Most of this expense is driven by the fact that it’s one of the rarest elements found on Earth, only an estimated 0.0002 parts per million (2 × 10⁻¹⁰) of the crust are made of this. But it’s use in catalytic converters has brought about a bigger demand of recent years, hence the price has rocketed. The crystal structure of pure Rhodium is face centred cubic, like gold, and it doesn’t found in many minerals (as it’s both rare and quite unreactive). However, there is this very rare mineral Bowieite – which is a rhodium sulphide (though the rhodium in the natural environment is sometimes substituted for platinum and iridium).

Where did the structure come from?

The structure of Bowieite was discovered by Parthé, Hohnke and Hulliger in 1967, and was only later named after the mineralogist Stanley Bowie (not David Bowie).

A mineral that came down to Earth – pyroxferroite

What does it look like?

The crystal structure of pyroxferroite, the blue tetrahedra are the silicate units which form chains along the structure.

What is it?

So today is Buzz Aldrin’s birthday – Happy Birthday Buzz! Inspired by his and other exploits on the moon we’re featuring a mineral that at one point was only thought to occur on our lunar neighbour.

The Apollo missions, 6 in all, brought back nearly 400 kg of rock which was laboriously studies on its return to earth. In these samples three new minerals were identified – armalcolite, pyroxferroite and tranquillityite. At the time each were thought to be unique to the moon but over the years have all been identified in Earth (and Martian) rocks. The last of these moon minerals to be found terrestrially was tranquillityite, which was discovered in a rock from Western Australia in 2012.

Pyroxferroite is classified as an inosilicate mineral, meaning that it has a chain (or backbone) of silicate tetrahedral running through it that are all connected. In between the chain can be found iron, and calcium atoms. Since its discovery in the Apollo rock collection it has been found in rocks from all over; Japan, Sweden, USA and even a rock from Mars.

Where did the structure come from?

The structure of pyroxferoite was found by Burnham in 1971, and is #9012889 in the Crystallography Open Database.