Crystal Purity Testing Methods (Taking Quartz as an Example):
Visual Inspection: High-purity crystal (e.g., SiO₂ ≥ 99.9%) is transparent and free of impurities; lower-grade crystals contain bubbles or cracks.
Instruments:
X-ray Diffraction (XRD): Quantitative analysis of mineral composition (error ±0.5%).
FTIR Infrared Spectroscopy: Detects impurities such as hydroxyl groups (e.g., OH⁻ content < 10 ppm in synthetic crystals).
Density Method: Pure crystal density is 2.65 g/cm³; a deviation > 0.02 g/cm³ indicates the presence of impurities.
Example: The purity of fused quartz can reach 99.99%, while natural crystal is typically 99.5%-99.9%.
