With this screening tool, it is possible to reliably determine whether diamonds, rubies and sapphires are of natural origin or synthetically produced gems, and whether they were subjected to value-enhancing measures. The device operates with four different filters to determine the value of the test specimen at hand. The battery-powered GemPen is resilient and comes with a travel case which, like the tool itself, guarantees safe and correct usage due to its shapes, surfaces and graphics.