Trigonal trapezohedral (chiral space groups P3₁21 / P3₂21)
hardness
7.0 Mohs (defining mineral)
density
2.648 g/cm³
phase transition
α- to β-quartz inversion at 573 °C (1 bar)
Core Principles & Analysis
Pierre and Jacques Curie discovered the direct piezoelectric effect in quartz in 1880, and Walter Guyton Cady built the first quartz crystal oscillator in 1921; AT-cut quartz wafers resonating at 32,768 Hz (2¹⁵ Hz) keep time in billions of watches and computers.
Built from corner-sharing SiO₄ tetrahedra in chiral helices lacking a center of inversion, low-temperature α-quartz transforms reversibly at 573 °C into hexagonal β-quartz.
High-purity electronic-grade quartz crystals are grown hydrothermally inside steel autoclaves at ~350–400 °C and 1,000–1,500 bar using alkaline solutions to dissolve nutrient silica onto oriented seed plates.