appear glassy, 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 Reddish color; 5-6 curved, conchoidal fracture; may appear glassy, greasy, resinous, or dull Quartz White Curved, 7 conchoidal fracture; occurs as _rose quartz_, as pink _chert_, and as _agate_ and _jasper_ 14. NONMETALLIC luster, PURPLE or VIOLET color