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SHORTLY before Lynn Sugarman of Teaneck, N.J., bought her summer home in Lake George, N.Y., two years ago, a routine inspection revealed it had elevated levels of radon, a radioactive gas that can cause lung cancer. So she called a radon measurement and mitigation technician to find the source.
DETECTION Using devices like the Geiger counter and the radiation detection instrument Stanley Liebert measures the radiation and radon emanating from granite like that in Lynn Sugarman’s kitchen counters.
“He went from room to room,” said Dr. Sugarman, a pediatrician. But he stopped in his tracks in the kitchen, which had richly grained cream, brown and burgundy granite countertops. His Geiger counter indicated that the granite was emitting radiation at levels 10 times higher than those he had measured elsewhere in the house.
The minerals that are found in granite are primarily quartz, plagioclase feldspars, potassium or K-feldspars, hornblende and micas. Quartz is usually the last mineral to crystallize and fills in the extra space of the other minerals. Quartz's hardness, lack of chemical reactivity and near lack of cleavage give granite a significant amount of its desirable durable properties. The quartz will appear gray, but is actually colorless and is reflecting and fusing the colors of the white and black minerals surrounding it. The plagioclase feldspars are generally white with a porcelaneous luster. The K-feldspars are generally the ones that give granite its color variations from yellow to orange to pink or blue. Dark K-feldspars can give granite its black varieties as well. The micas are generally muscovite (silver), biotite (black or brown) or lepidollite (violet or pink) and provide the sparkle that some granites possess. The hornblende and biotite provide granite with the black pepper portion of the famous and distinctive "salt and pepper" look to classic granite.
Some accessory minerals include gemstones such as tourmaline, beryl, topaz, zircons and apatite. These minerals are generally scattered in the groundmass and generally do not affect the overall appearance of the stone. Other accessory minerals are important economically such as phosphates and rare earth oxides. Related to the rare earth elements is a significant concentration in granite of the element uranium. Granite is actually rather radioactive and has 5 to 20 times the concentration of uranium compared to other common rock types. Some health concern exists in areas that are rich in granitic terrain, as background radiation is enhanced by the presence of large granite bodies. Although the uranium is generally not concentrated enough to make granite a uranium ore, the leaching and erosion of granite has helped produce most of the uranium ore deposits around the world.