Mohr-Coulomb Faulting Simulator (2D)

Real fractures in the crust do not form on the plane of maximum shear stress — they form where shear stress first overtakes the rock's frictional strength, on planes predicted by the Mohr-Coulomb failure criterion. This 2D companion renders the Mohr circle directly: a live circle built from the principal stresses σ1/σ3 against a failure envelope built from cohesion and internal friction angle, plus a rock cross-section that fractures the instant the circle touches the line. Switch between normal, reverse and strike-slip Andersonian regimes, tune the stress state, and use "snap to optimal" to see the Coulomb-predicted fracture angle θ = 45° + φ/2 from σ1 — why real conjugate faults cluster around 32–52° from σ1 instead of the naive 45°.