Quantitative microstructural analysis of petrographic thin sections often requires separate instruments and workflows for grain segmentation, mineral identification, and crystallographic orientation. Here, we present a largely automated workflow that derives these measurements using only a conventional rotating-stage polarizing microscope and camera. The workflow begins with the acquisition of a continuous 360° video of a thin section under crossed polars during manual rotation of the microscope stage. The video is automatically converted into a maximum- intensity image and an extinction-angle map, from which grains are segmented based on differences in optically inferred c-axis orientation, and grain size, shape, and grain-shape orientation are quantified. The resulting grain segmentation also enables semi-supervised mineral classification from a limited number of user-labeled grains. For low-retardation uniaxial minerals, additional λ-plate measurements and a small stage tilt resolve optical ambiguities and provide three-dimensional c-axis orientations. Comparison with electron backscatter diffraction shows that the optical workflow reproduces grain boundaries, grain-scale statistics, and c-axis fabrics most reliably for thin sections approximately 20–35 μm thick and with a 5° segmentation threshold. Its main limitations arise from boundary mixing in thicker thin sections and weak optical contrast between neighboring grains. The workflow is implemented into NicoNavi, which integrates phase classification, grain morphology, and crystallographic orientation within a common grain-scale dataset. This approach provides a practical framework for reproducible quantitative petrography using conventional thin sections without specialized microanalytical instrumentation such as electron backscatter diffraction.