What term refers to the pattern shown by certain gems when viewed through a spectroscope?

The term that refers to the pattern shown by certain gems when viewed through a spectroscope is indeed the absorption spectrum. When light passes through a gemstone, some wavelengths of that light are absorbed by the stone's molecular structure, while others are transmitted. This selective absorption creates a characteristic spectrum that can be analyzed to identify the gemstone and determine its properties.

In the context of gemstone analysis, the absorption spectrum is highly valuable because different elements and compounds absorb specific wavelengths of light, resulting in unique patterns. These patterns serve as fingerprints for gems, aiding in identification and differentiation.

The absorption spectrum stands apart from reflection patterns, which involve the way light reflects off the surface of a gem, and birefringence, which pertains to how light behaves as it passes through double-refractive materials. An interference pattern, while important in optics, pertains to light waves interacting and does not directly represent the absorption characteristics of a gemstone.