Presidium Gem Tester II – Thermal Conductivity Scale and Semi-Precious Gemstones

I have a small, compact device that helps me determine the authenticity of the beads and gemstones I sell. The machine is called a Presidium Gem Tester II. It runs on electricity or battery power (2 AAs). The technique is called thermal conductivity scale (TCS) testing. The scale reads Glass at one end (left side) and Diamond/Moissainte (right side) on the other. In between glass and diamond is a number of other semiprecious gemstones, including garnet, tourmaline, iolite; chyrsoprase, emerald, nephrite (greens); tanzanite, aquamarine; quartz, amethyst, citrine; jadeite, spinel; topaz; ruth, sapphire. (The red CAL stands for calibrate.)

To help me “measure” and record a reading of the thermal conductivity of the stones, I have decided to give them values from 0 – 6 (see the arched bars on top, like a rainbow). The first arched bar on the top left I will call value 1, next to the right is 2, and so on, until we get to the far right, which is 6 for diamond/moissanite. I will test three times, and use different beads from the same strand.

Each value (1-5) will be divided into quarters. So each stone will have a reading of a whole number (e.g. aquamarine could read as 2.0), or a portion of a whole number (e.g. jadeite could read at 2.75).

I will keep this listing updated as I test new stones.

AGATE: Bamboo Leaf (matte), 2.0; Black banded agate, 2.0; Yellow Fire Crackle Agate, 1.75

(An observation about agate: When the bead is broken, it looks like a glass substance. It is very shiny.)

AMETHYST (purple quartz): 2.5

CITRINE (yellow quartz): 2.5



MOONSTONE: white with blue flash, rainbow, 0 – 0.25

QUARTZ (clear): 2.5




TIGER’S EYE: Natural matte, 2.25

Testing the stone with the Presidium isn’t the only test I do to determine authenticity. There are other ways to examine beads, too!

If you would like to see my jewelry and gifts, check out “Gentle Angel Treasures” on Facebook and Instagram (@gatreasures).

Angela G. Gentile


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