Aluminous minerals-corundum, andalusite, iron-cordierite, spinel, (hercynite), and tepaz-are found in protolithionite-topaz-banded strings with a width ranging from 1 cm to 15 cm in fine-grained granite at Yagenyama., Many parallel strings are found, each keeping a distance from 10 cm to 1 m., The granite is quite characteristic and contains a high content of quartz, some parts of which are of secondary origin in connection with greisenization., Partly the granite is altered to greisen near the contact with strings., In general the biotite is a later constituent than some of quartz., These biotite crystals showing greenish brown pleochroism often project into miarolitic cavities which are filled with feldspars., Besides, there is another type of biotite showing dark brown pleochroism, which although in a small quantity, crystallized under the normal granitic condition., Zoning arrangement of minerals in the strings is distinct., The marginal zone consists of acidic oligoclase (of the composition of Ab₈₇An₁₃), to some extent altered to sericite., The next zone consists of andalusite, corundum (sometimes iron-cordierite), and protolithionite., The central zone consists of topaz, protolithionite and sometimes zinnwaldite and graphite., A chemical analysis of the protolithionite is given in the table 4., Orthoclase-quartz-protolithionite-pockets are also found near the strings., The formation of these strings is due to a metasomatic origin, chiefly pneumatolytic, by mineralizers rich in fluorine or aluminium fluoride gas., The pockets are metasomatized pegmatite-druses., At first orthoclase was replaced, being more unstable than albite at the pneumatolytic stage, and corundum, andalusite, iron-cordierite, muscovite, and protolithionite were formed by addition of FeO concentrated in the residual magmatic liquid as hydroxyl-bearing silicate or hydrate., Later albite, andalusite, and cordierite were again replaced by topaz and protolithionite : spinel and corundum occur also as replacement products of this stage., Large sapphire crystals were produced by pneumatolysis independently., Wolframite-quartz veins, somewhat later derivatives, running in the elongated direction of the strings are related to the formation of the strings., Another same set of strings and veins running in a different direction are also found near Sengeyama.,