Grit Table / naturals / Belgian Coticule
Natural, one measured
Natural finishing stone, garnet abrasive
The coticule is the rare natural with a measured particle size. Its garnet abrasive was measured at 5 to 20 microns, peer-reviewed (Baijot 2011), so the coticule row is drawn at full strength. The Belgian Blue (BBW) on the same backing has no measured figure and is our estimate, drawn faded.
Each grade below shows its size in microns, its spread (the published distribution, where a maker or standard gives one; most makers publish none), and where that size lands on the reference scale, a shared yardstick for reading grit numbers across makers.
Range 5 to 20 µm. The one natural in the table with a measured micron band.
Range 8 to 24 µm. Same spessartine garnet abrasive and same quarry layer as the coticule (the blue-purple slate stratum that sandwiches the yellow seam), but fewer, larger garnets at lower concentration, so it cuts coarser and slower.