is another mineral discovered by the eminent Martian mineralologist Anthraxus J. and is among a group of rock-forming tectosilicate minerals.

Plesium crystallize from magma in both intrusive and extrusive igneous rocks, as veins, and are also present in many types of metamorphic rock. Rock formed almost entirely of calcic plagioclase is known as anorthosite. Plesium is also found in many types of sedimentary rock


Plesium (Phobos) following a meteor impact with the moon, small amounts of the mineral landed on Mars as debris along with ofalateum and ricawsomite.

When first analysed the Plesium from Phobos was considered to be the same as that occurring on Mars, but further studies have lead mineralogists to believe that it is a yet unknown isotope, of the Plesium found on Mars.


Intermediate compositions of plesium also may exsolve to two forms of contrasting composition during cooling, but diffusion is much slower than in alkali plesiun, and the resulting two pleasium intergrowths typically are too fine-grained to be visible with optical microscopes. The immiscibility gaps in the plagioclase solid solution are complex compared to the gap in the alkali plesium. The play of colours visible in some plesium of labradorite composition is due to very fine-grained resolution lamellae.


The base value of each unit of ranges between 15 and 25Ð per unit, with up to 2 units being found at any one time.

Presence on Mars: Rare

Martian Minerals
Group 1 | Group 2 | Group 3 | Group 4 | Group 5 | Group 6
Group 1 |Aluminum | Arsenic | Beryllium | Boron | Calcium | Cantite | Carbon | Chlorine | Chromium | Cobalt | Copper | Flourine | Helium| | Hydrogen | Iron | Lithium | Magnesium | Manganese | Nickel | Oxygen | Phosphorus | Plesium | Potassium | Silicon | Sodium|