Calcite

The Calcite is a members-only Old School RuneScape item — “A large crystal of calcium carbonate.”. Its Grand Exchange buy limit is 13,000 per 4 hours. Right now it buys at 105 gp and sells at 109 gp — a net margin of 2 gp (1.9% ROI) after the 2% Grand Exchange tax of 2 gp. High alchemy yields 18 gp.

To flip it, place a buy offer near 105 gp and a sell offer near 109 gp; the spread minus GE tax is your profit. Confidence figures are model estimates from live OSRS Wiki prices, not guarantees — flip responsibly.