pencil ore

pencil ore

[′pen·səl ‚ȯr]
(geology)
Hard, fibrous masses of hematite that can be broken up into splinters.
References in periodicals archive ?
Much high-quality hematite, including "kidney ore" and "pencil ore," and also fine specimens of quartz, calcite and barite were recovered.
Here also was found the finest "pencil ore" hematite, a material which, because of its structure, could be broke into long, thin, pencil-like fragments.