PRECIOUS CORAL 121 



of the common species being mushroom coral, stag- 

 horn coral, star coral, brainstone, and flexible coral. 



The precious coral, or coral of commerce, is not 

 found in such enormous quantities as the species 

 listed above. This coral differs from the common 

 corals, for the solid, brilliantly colored calcareous 

 skeleton is deposited as a supplementary basis out- 

 side the tissues. The colonies of precious coral branch 

 out and appear to grow as a plant or vine. The coral 

 branches, however, do not seek the light as plants 

 do, but spread horizontally along the main stem or 

 trunk, which consists of the lime carbonate secreted 

 by coral polyps which lived many years ago, and 

 is very hard and stone-like in appearance. The 

 branches are covered with a thin, fleshy, reddish rind 

 in which live polyps are embedded. The slender ends 

 of the branches are so soft that they can be easily 

 cut by a knife, since the polyps in this part of the 

 branch have not yet secreted much calcium car- 

 bonate. As the coral branch becomes older, these 

 polyps secrete their carbonate, thus forming the 

 stone-like precious coral. 



Precious coral is obtained by trimming, cutting, 

 and polishing the branches of coral taken from the 

 ocean bottom. Since it has about the same composi- 

 tion as the mineral calcite, which is composed of 

 crystalline calcium carbonate, it has approximately 

 the same hardness and density as this mineral. Com- 

 pared to the precious stones, coral is rather soft, but 

 as it possesses some toughness and tenacity it wears 

 fairly well. Although it scratches easily, the 



