What does "sinter" mean?

Sinter: Dross, as of iron; the scale which files from iron when hammered; -- applied as a name to various minerals. Calcareous sinter, a loose banded variety of calcite formed by deposition from lime-bearing waters; calcareous tufa; travertine. -- Ceraunian sinter, fulgurite. -- Siliceous sinter, a light cellular or fibrous opal; especially, geyserite (see Geyserite). It has often a pearly luster, and is then called pearl sinter.