streak
...that the streak of a mineral, the color of the mark it makes when rubbed on a plate, is usually a more consistent identifier than the color of the original mineral?
...that the <b id="mwA4w"><a href="./Streak_(mineralogy)" id="mwA40" rel="mw:WikiLink" title="Streak (mineralogy)">streak</a></b> of a <a href="./Mineral" id="mwA44" rel="mw:WikiLink" title="Mineral">mineral</a>, the <a href="./Color" id="mwA48" rel="mw:WikiLink" title="Color">color</a> of the mark it makes when rubbed on a plate, is usually a more consistent identifier than the color of the original mineral?