Calcite Dichroscope GI-7208
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Basically GI-7208 Calcite Dichroscope is a tool that lets you view the different colours of a dichroic piece of rough. It shows whether or not a stone is dichroic (reflects 2 colours). This can be helpful in differentiating stones of the same colour from one another. Dichroscopes can be useful with identifying gemstones that are still in the rough and when stones are set and difficult to get to with other instruments. Light entering the dichroscope is broken into two polarised rays that have vibrational directions at right angles to each other. The two images in the dichroscope represent the polarised light and the pleochroic colours signifies doubly refractive stones except if the stone is viewed thru the optic axis. Single colour in the dichroscope represents singly refractive stones. There are several different types of Dichroscopes, but the most common type is one made with Calcite. It is used by most people for identifying whether a piece of rough is dichroic. The advantage of the dichroscope is that the two pleochroic colours that may be characteristic of a given direction in a doubly-refractive gem are seen side by side. If no dichroism is identified in the first assessment, the stone can be turned and viewed in other directions. Trichroic stones like Andalusite will show all three, just two at a time while you rotate the rough, you will see three colours. Trichroic gems can also be distinguish and will reveal three colours if the stone is viewed in three directions perpendicular to each other.
You place the mineral in front of the instrument and direct it toward a light source. Then you compare the two images. Make sure to observe the mineral in different directions.
Both images stay identical this means that the mineral is isotropic, amorphous or micro cristallic.
When you observe two different colours then the mineral is double refracting and belongs to the group of uniaxial cristallic systems.
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