The
other varieties differ in composition in the proportions of their
constituents, and some possess an admixture of other substances. The
spinel and balas ruby are of similar composition. The red spinel on
being heated becomes brown, but more opaque on cooling. As the
heat declines it changes to green, then passes to an almost colourless
state, and finally resumes its pristine colour. With borax or salt of
phosphorus it melts into a glass, more or less coloured by chrome or
iron. It is soluble in powder when heated in sulphuric acid.
The rubicelle is the variety having an orange colour, approaching that of the jacinth.
The violet spinel also bears the name of the alman-dine ruby.
