Experts Cut Rock Into Slices

Wanganui Chronicle, Volume 83, Issue 56, 8 March 1939, Page 11

Experts Cut Rock Into Slices

BOSTON. No matter how thin you slice it, it Mill—rock. Geological Survey specialists have developed a technique for slicing the toughest, hardest boulder thinner than the proverbial restaurant beefsteak. Actually, the thinness ffleasuree but one one-thousandth of an ir :h. Only three or four laboratories in the United States are able to dupli” cate tho process used in Washington, and the only foreign competition is from three laboratories located in England, Germany and Norway. Thinner than tissue paper and far more transparent, tho specimens are mounted on microscope slides. Between three and four thousand specimens are cut, ground and polished every year, the Survey in most cases 1 being asked to determine the mineral content of the rock from which th® specimen camo. This is a far cry from the old-time prospector’s hit-and-miss selection of mineral lands. Making of Slides The making of microscope slides ot rock sections is an occupation as de* licate as tho jeweller’s and as obscure as the curling of willow plumes. Slicers Frank Beed and John Mergner learned their trade as apprentices of a naturalized Dane who was employed by the Geological Survey 20 years ago. He learned how in Norway. No slicing job is too difficult for them. Take a husky boulder from the rocky gorge of Grand Canyon for instance. The geologist tramping tho gorge knocks off a sample with his prospector's pick and sends it to Beed and Mergner in Washington. With their rock saws they slice a piece from the sample, preferably a very small piece. This is ground with carborundum powder of varying degrees of courscness and fineness until a smooth surface is attained. The surface is then cemented with Canada balsam to a glass slide. Next, the other side of the specimen is ground until it reaches the required thinness of one one-thousandth of an inch. Finally a protecting glass cover is cemented with balsam to the exposed surface and th* slide is ready for study. G-ems From Fairyland Minerals and rocks may be just jagged, unattractive masses when viewed in their natives form, but under the microscope, ground and polished, they .ako on the gay, transparent qualities jf gems from fairyland. Under the powerful lenses of the microscope they how patterns and designs more intriate than snowflakes, with colours briliant and varied. In addition to preparing thin »ec« ions of rock, these skilled technicians x’so prepare mounts of polished ores for dudy by reflected light. Such things .3 gold flecks smaller than one one-mndred-thousandth of an inch can be letected and examined. Recently n specimen valued at 75 lollars was brought into the grinding aboratory by a young geologist reurning from a field trip for the Geological Survey. It showed tho highest gold content and was the most valuable specimen to come into the laboratory in