The corundum group of gemstones - ruby and sapphire

Minerals in the corundum group has a very simple chemical compositionm, being an oxyde of aluminium, with the formula Al2O3. Corundum is found as barrel-formed crystals. Corundum is the second hardest mineral on earth, having a hardness grade of 9. Corundum and corundum gemstones can be made syntetically by melting aluminium in a flame of burning oxygen-hydrogen with a surplus of oxygen.

Such artificial rubies and sapphires are rather cheap, but have a good quality. They will however lack some of the intriguing impression upon the visual senses that natural stones have, due to the play caused by myriads of various elments included in natural stones.

Corundum often contain disolved elements giving colour to the crystal. Corundum without distinct inclusions and without uneven colour is used as gemstones. Corundum crystals of a distinct colour are more valuable than clear crystals. Corundum gemstones most often originate from the far east, for example Thailand, Burma and Sri Lanka.

Corund that do not have gemstone quality is widely used as abrasives and polishing tools.

Rods of ruby are used in lasers that make a red beam. The first lasers produced had ruby rods. The rod has a fully reflecting mirror in the back end and a halfly reflecting mirror in the front end where the beam comes out. Around the rod is an arrangemnt that makes light. The light is first absorbed in the chromium atoms found as additives in the ruby rod, giving these atoms higher energy, and then light is emitted again. Emitted light going back and forth between the two mirrors trigger more light to be emitted from the atoms and in a direction along the rod, thus making a concentrated beam.

Ruby or Rubine: Red corundum is called ruby or rubine, and is considered the most valuable corundum gemstone. The colour may vary from deep red, often found in rubines from Thailand and Burma to lighter red often found in rubines from Sri lanka. Rubine red as blood from a pidgeon are often considered the most valuable. Big rubines of good colour quality and without macroscopic inclusions are very rare, and these may get nearly the same prize as diamonds of the same size. The red colour of rubine originates from disolved chrome.

Blue Sapphire: Corund of blue colour is called saphire. Blue saphire is mostly called only saphire. The blue colour originates from small amounts of iron and titanium.

Saphire of other colours: Green, yellow, clear or orange corund of gemstone quality is also called sapphire.