Question

what temperature, pressure, time is required for quartz to form

Answer 1

There is no single "temperature, pressure, time" that universally produces quartz (SiO2). Quartz forms in many environments (igneous, hydrothermal, metamorphic, diagenetic) under a wide range of P–T–time conditions. Key points and typical ranges:

- Stability limits:
- Quartz is the low‑pressure polymorph of silica. At high pressures it converts to coesite (~>2.5–3 GPa, ≈25–30 kbar) and at still higher pressures to stishovite (>~8 GPa, ≈80 kbar). So “quartz” is stable below roughly a few GPa, depending on temperature.
- Quartz melts at roughly 1650–1720 °C at low pressure (melting point varies with pressure/composition).

- Typical formation environments and representative P–T–time ranges:
- Hydrothermal veins and late‑stage magmatic fluids: T ≈ 50–400 °C (commonly 100–300 °C), pressures from near‑surface fluid pressures up to a few hundred MPa (bars → 100s of MPa). Precipitation can occur over hours–years–thousands of years depending on fluid flux and saturation.
- Igneous crystallization (silicic magmas): T ≈ 650–900 °C (quartz joins the liquidus as magmas evolve), pressures typically 0–1 GPa (shallow to mid crust, often a few 100 MPa). Crystallization/cooling times from 10^2–10^6 years (depends on intrusion size and cooling rate).
- Metamorphic quartz growth (regional metamorphism): T ≈ 300–750 °C, pressures ≈ 0.2–1.0+ GPa (2–10+ kbar). Recrystallization/growth over 10^4–10^7 years.
- Diagenetic and sedimentary quartz (silica cement, authigenic quartz, chalcedony): T ≈ ambient to 200 °C, low pressures of burial (bars to tens of MPa). Timescales typically 10^3–10^7 years (opal/opal-A to microcrystalline quartz conversion can be slow at low T).
- Microcrystalline quartz (chalcedony, agate): often forms at lower T (tens to a few 100 °C) from silica‑rich fluids; growth rates can be slow (years to many thousands of years).

- Kinetics matter: temperature and pressure set thermodynamic stability, but nucleation and growth depend on silica concentration/supersaturation, fluid chemistry (pH, dissolved ions), presence of surfaces/impurities, and time. High supersaturation and nucleation sites can produce rapid precipitation even at relatively low T.

Short summary: quartz can form from near‑surface temperatures (tens of °C) up to several hundred °C in hydrothermal/diagenetic settings, and up to ~900 °C in magmatic contexts; pressures from near‑atmospheric up to the low–moderate crust (tens to a few hundred MPa, up to ~1 GPa) produce quartz — beyond ~2.5–3 GPa it converts to coesite. Timescales range from hours–days (under highly supersaturated hydrothermal conditions) to millions of years (metamorphic/diagenetic/igneous processes).

If you have a specific context (e.g., hydrothermal vein, granite, regional metamorphism, diagenetic cement), tell me which and I can give more focused P–T–time ranges and examples.