Strike and Dip

Strike is the compass bearing of the horizontal line formed where a tilted rock layer, mineral vein or fault plane intersects a horizontal surface; dip is the angle that same plane inclines downward away from the strike line, measured at right angles to it. Together the two figures describe, precisely and repeatably, which way a sloping geological feature runs and how steeply it descends.

How it forms

Strike and dip are not something that forms in their own right -- they are simply the geometry left behind by whatever tilted or fractured the rock. Sedimentary beds laid down flat can be folded and faulted by later tectonic movement, ending up dipping at an angle; mineral veins are even less likely to be perfectly vertical or horizontal to begin with, since they form by filling fractures whose orientation is controlled by the regional stresses acting on the rock at the time. Either way, once a layer or vein is anything other than flat, it has a definable strike and dip.

Why minerals concentrate here

Strike and dip do not themselves explain why ore concentrates -- that is a question about mineralisation, not orientation -- but they explain why economic deposits are so rarely worked as simple flat sheets. A vein fills a fracture that is inclined almost by definition, and a once-flat sedimentary seam is often tilted by the same tectonic activity that helped mineralise it in the first place. Knowing a deposit's strike and dip is what lets a mine follow it reliably, rather than rediscovering it by chance at every new working.

Typical shape of the deposit

Applies to planar or roughly planar bodies -- a vein or lode, a bedded seam, a fault plane -- rather than to a pipe, disseminated deposit or placer, none of which have a single strike and dip to measure.

What this means for mining

Once a lode's strike and dip are known, they directly shape how a mine is laid out. Levels are driven along the strike to stay within the ore as far as possible; crosscuts are driven across the strike, through barren ground, specifically to intersect a lode (or a fault) at a known point. Dip decides how a shaft reaches the ore: a shallow-dipping lode is usually reached by a vertical shaft with levels driven sideways to meet it, while a steeply dipping lode can instead be followed directly by an 'underlie shaft' sunk on an incline that matches the lode's own angle -- both approaches are recorded side by side in 19th-century Cornish mines. Traditional British mining practice measured dip not in degrees but as an 'underlie' expressed in feet per fathom of depth -- an 1856 survey recorded Dolcoath's main lode as running close to east-west and dipping 2 feet south in the fathom, and Condurrow's as running 5 degrees north of east and dipping 18 inches in the fathom -- the same strike-and-dip information geologists record today, in a distinctly Cornish form of words.

Sources

1. (secondary) 1856 Mines in Devon and Cornwall — Grace's Guide
2. (secondary) Strike and dip — Wikipedia

Record created: 1 September 2026 · Last researched: 1 September 2026