Core angle:

In geology, mining, and civil engineering, internal core angles refer to a geometric measurement system used to calculate the exact, true 3D orientation of subsurface structures (such as fault lines, rock layers, or mineral veins) from a cylindrical rock sample extracted during diamond core drilling.

Because the drill rig itself is often tilted, geologists cannot measure the rock layers using a standard compass alone. Instead, they measure the angles that a feature makes relative to the cylinder’s own geometry and then convert them into real-world geographic coordinates (strike and dip). The Three Primary Core Angles

When a planar geological structure intersects a cylindrical drill core, it cuts through it diagonally, creating an oval or ellipse shape. Geologists measure three core angles relative to this ellipse:

Alpha Angle (α): The acute angle (0° to 90°) formed between the central longitudinal axis of the core cylinder and the long axis of the intersection ellipse. This angle can be measured on any piece of core, even if the absolute direction of the drill hole is not known.

Beta Angle (β): The radial angle (0° to 360°) measured clockwise around the core’s circumference. It spans from a known reference line—most commonly the Bottom-of-Hole (BOH) line—to the lowest point (apex) of the intersection ellipse.

Gamma Angle (γ): The linear angle measured directly on the flat surface of the geological plane itself. It measures the distance between the long axis of the ellipse and any linear stretch marks or slip lines (lineations) on the rock. Alternative Contexts

Depending on your industry, “core angle” can mean a few other distinct things: Roger Marjoribanks Measuring Structures in Oriented Core – Roger Marjoribanks