| The function of the microscope is to enlarge | | | | but, in the natural one, the growth lines are |
| objects so as to make them more easily visible | | | | straight and set at definite angles. This latter |
| to the human eye. Its use in science is unlimited, | | | | feature is an important characteristic of most |
| and to the gemologist the microscope is more | | | | natural mineral crystals. The microscope can |
| important than any other instrument. This is | | | | provide all-important clues in the identification of |
| because one of the biggest problems in modern | | | | rubies and sapphires. |
| jewelry is the detection of synthetic and imitation | | | | A gem stone that may set an even bigger |
| stones, and without a microscope the task would | | | | problem is the emerald. In this case, synthetic |
| be almost impossible. | | | | stones are internally also remarkably similar to the |
| The detection of imitation stones covers a vast | | | | natural ones. Fortunately, Chatham's synthetic |
| field and the following lines serve only as an | | | | emeralds do have a lower specific gravity and |
| introduction. Three out of four of the most valued | | | | refractive index than the natural stones, but it is |
| gem stones can be produced synthetically in the | | | | not always possible, if a stone is set in a piece of |
| laboratory. These are the ruby, the sapphire, and | | | | jewelry, to apply these tests. Here the |
| the emerald. Needless to say, the difference in | | | | microscope is useful again. |
| value between a natural and synthetic stone is | | | | Natural emerald possesses cer¬tain internal |
| enormous, and it is therefore of greatest | | | | features called inclusions. Some of them take the |
| importance to the jeweler that he can be sure | | | | form of spiky cavities filled with tiny mineral |
| they can be effectively distinguished from each | | | | crystals and gas bubbles. Indeed, they are so |
| other. | | | | typical that they can be associated with definite |
| Synthetic rubies made by the flame-fusion | | | | mining localities and thus form an important guide |
| process are in all their physical properties almost | | | | to the origin of some emeralds. Chatham's |
| identical with the natural stone. Chemically, both | | | | synthetic emeralds also possess special inclusions, |
| are crystalline aluminum oxide. The red color is in | | | | and under the micro¬scope, these look rather |
| both cases produced by minute quantities of | | | | like a fine pattern of lace. They actually consist of |
| chromic oxide, and if synthetic and natural rubies | | | | minute interweaving channels filled with liquid and |
| are tested for their specific gravity, refractive | | | | thus are very different in character from the |
| index, and absorption spectra, the same results | | | | inclusions of the natural emeralds. |
| occur in both cases. Yet, if they are placed under | | | | A simple magnifying glass that enlarges ten times |
| a microscope, a marked difference between the | | | | can also be a valuable aid in the identification of |
| two is found. What then are these internal telltale | | | | some gem stones. Thus, a colorless zircon might |
| features that will enable us to distinguish the real | | | | well be confused with a real diamond, but if both |
| from the synthetic? | | | | are carefully examined with a hand lens by looking |
| Fine curved lines are immediately noticeable that | | | | through the top of the stone at the rear facets, |
| are rather like the grooves of a phonograph | | | | everything at the back of the zircon will appear |
| record and run through the stone. There are also | | | | double, thus revealing its strong light-splitting |
| some black spots interspersed irregularly | | | | property. |
| throughout the gem. The curved lines are known | | | | Since a diamond belongs to the cubic crystal |
| as growth lines, and they are produced during the | | | | system, letting light rays pass through without |
| formation of the synthetic boule and are a certain | | | | splitting them, the double image will not be shown |
| sign that the stone is synthetic. The black spots | | | | by it. This is one simple test that immediately |
| represent tiny bubbles of gas, and these, too, | | | | distinguishes between these two gem stones. |
| were included in the boule during its formation. | | | | There is one direction along the so-called optic |
| Gas bubbles and curved growth lines are | | | | axis of a double-refractive stone where the light |
| therefore typical characteristics of synthetic | | | | rays are not split and the doubling effect cannot |
| corundum. | | | | be seen. It is therefore wise to tilt the gem a little |
| But, what does the inside of natural corundum | | | | when examining it with a lens to insure that the |
| look like under the microscope? Again, there are | | | | optic axis does not lie at right angles to the table |
| the curved growth lines in the synthetic stone, | | | | facet. |