Where ( n ) is the refractive index (RI).
[ n(\lambda) = A + \fracB\lambda^2 ]
| Property | Physical Principle | Example | | :--- | :--- | :--- | | Brilliance | Total internal reflection (Snell’s Law) | Diamond | | Fire | Dispersion (n vs. wavelength) | Cubic Zirconia | | Color | Crystal field splitting (d-electron transitions) | Ruby (Cr³⁺) | | Glow under UV | Photoluminescence (Stokes shift) | Fluorescent diamond | | Color change with rotation | Pleochroism (anisotropic absorption) | Tanzanite | | Star effect | Scattering from oriented inclusions | Star sapphire | age18a physics of gemstones
The Age18a lab typically uses a polariscope: two polarizing filters with a gem between them. As you rotate the gem, the intensity of light changes, proving the anisotropic nature of the crystal.
[ \sin(\theta_c) = \fracn_2n_1 ]
The symmetry of a crystal lattice is described by its point group, which defines the arrangement of atoms in three-dimensional space. For example, the crystal structure of quartz is hexagonal, with a six-fold symmetry axis. This symmetry is responsible for quartz's piezoelectric properties, which make it useful for applications such as oscillators and sensors.
This absorption is governed by quantum selection rules. Interestingly, the same chromium in a different crystal (e.g., beryl, which becomes emerald) produces a different color because the crystal field strength changes the energy gap. Where ( n ) is the refractive index (RI)
In the , this is taught using the Cauchy equation :