greasy, resinous, or dull D. Cannot be scratched by an ordinary pocket knife but can be scratched by quartz Feldspar White Glassy or pearly 6 luster; good cleavage in 2 directions that meet at an angle of 90° or near 90° Garnet White Commonly occurs 6½-7 as crystals Opal White Curved, 5-6 conchoidal fracture; may appear glassy, greasy, resinous, or dull Quartz White Curved conchoidal 7 fracture; brownish-yellow _smoky_ quartz crystals commonly 6-sided prisms with pyramid-like ends; _chalcedony_ and _jasper_ may be a shade of yellow, too 9. NONMETALLIC luster, BROWN color