present inventor therefore has conducted the following experiments and confirmed the fact that the permanent electric poles of tourmaline are extinguished at 950 u00b0 to 1000 u00b0 c the experiments will now be described below roughly igneous rock produced in kamaishi containing about 8 to 10 of iron tourmaline was crushed into stones of about 5 to 10 cm from which the crushed stones having a large content of tourmaline were selected visually and were used for the experiment copper sulfate was dissolved in an amount of 2 g in 1000 cc of purified water deionized water to obtain a bluish solution due to copper ions 500 grams of the crushed stones containing the tourmaline were immersed in this solution and were left for 24 hours the blue color due to copper ions disappeared and the solution became colorless and transparent after another three days the black tourmaline portions on the surfaces of the crushed stones changed into a green color this is the color due to a basic carbonate of copper 5h 2 o cuco 3 cu oh 2 which is so called patina this points to the fact that copper ions in the copper sulfate solution are electrically deposited on the portions corresponding to the negative poles of the tourmaline however no copper ion is electrically deposited on some exposed portions of the same tourmaline these portions are ones corresponding to positive poles that have the same electric charges as the copper ions which are cations the crushed stones were maintained at temperatures of 900 u00b0 c 950 u00b0 c 1000 u00b0 c and 1050 u00b0 c.