English: Sketches of uniaxial interference figures as might be created with a geological microscope. In these cases, the figures are viewed along the optic axis of each mineral. The colours approximate birefringence colours which might be seen if this were a mineral with second order maximum birefringence.The dark "maltese cross" pattern is characteristic of uniaxial minerals, and will not vary as the microscope stage is turned. Also shown are schematics of the shape of a cross section through the mineral's optical indicatrix (recording its refractive index in 3D) that would be seen at each position. The elongated direction could be distinguished by adding a sensitive tint plate to the microscope, letting the user discriminate between "uniaxial positive" (left) and "uniaxial negative" (right) minerals.