Mica is built from TOT sheets — a layer of octahedral Al/Mg/Fe sandwiched between two tetrahedral Si-O sheets. Inside a TOT sheet, every atom is locked in place by strong covalent Si-O bonds. Between TOT sheets sits a layer of interlayer cations (K+) held only by weak electrostatic and van der Waals attraction.
stress at crack tip = force × (0.3 + 1.7 × sharpness/100)
cleaves the instant stress > interlayer bond strength
Because the interlayer bond is roughly 50-100× weaker than the in-plane bonds, a wedge inserted at any interlayer gap propagates a crack across the entire crystal almost instantly — this is perfect basal cleavage. Click near the top of the stack to peel single ~1 nm TOT sheets (the same trick used to hand-exfoliate mica down to atomically thin flakes for van der Waals heterostructure research); click deeper to pop off a thicker flake in one piece.
- Splitting force / Wedge sharpness — combine into the stress delivered to the selected gap. A sharper wedge concentrates the same force into a smaller area, exactly like a real cleaving blade.
- Cleave mode — click a horizontal gap between sheets; once stress clears the interlayer threshold, every sheet above that gap comes off together as one flake.
- Shear mode — click inside a sheet and try to cut straight across it. Even at maximum force and sharpness the stress never reaches the in-plane threshold, so the sheet only develops ragged micro-fractures instead of cleaving cleanly — a direct demonstration of mica's extreme bonding anisotropy.
- Mineral choice — biotite's Fe/Mg substitutions weaken the interlayer bond further (easiest to flake but also the most brittle sheets); phlogopite's higher-temperature structure resists longer.