The idea of using Olivine has been promoted by the geochemist Prof. Schuiling.

The appearance of the wheels and their work was like a beryl and the four of them had one likeness and their appearance and their work was as it were a wheel within a wheel.

The appearance of the wheels and their work was like unto the colour of a beryl and they four had one likeness and their appearance and their work was as it were a wheel in the middle of a wheel.

I looked, and behold, four wheels beside the cherubim, one wheel beside one cherub, and another wheel beside another cherub and the appearance of the wheels was like a beryl stone.

And when I looked, behold the four wheels by the cherubims, one wheel by one cherub, and another wheel by another cherub and the appearance of the wheels was as the colour of a beryl stone.

Look at this diagram, which is showing warm waters in red, cool waters in blue, and on the continents, what you're seeing in bright green, is the growth of vegetation, and in olive green, the dieback of vegetation.