What is "sickle-gloss"

Sickle-gloss, or sickle sheen, is a silica residue found on blades suggesting that they have been used to cut the silica-rich stems of cereals and forming an indirect proof for incipient agriculture. The gloss occurs from the abrasive action of silica in both wild and cultivated stems of cereal grasses, meaning the occurrence of reaping tools with sickle gloss doesn't necessarily imply agriculture. The first documented appearance of sickle-gloss is found on flint knapped blades in the Natufian culture (12,500 to 9500 BC) in the Middle East, primarily in Israel.