Gusaba:Kurandura umwanda wicyuma mugihe gitose no kweza imyunyu ngugu itari metallic, nka quartz, sodium cyangwa potassium feldspar.Mubyongeyeho, hamwe nububasha bukomeye bwa magnetique, bigira ingaruka nziza cyane mugutandukanya imyunyu ngugu ya magneti idakomeye, nka hematite, spekulite, limonite, siderite, ubutare bwa manganese, nibindi.