Match the elements with its source rock The task is to match the lettered items with the correct numbered items. Appearing below is a list of lettered items. Following that is a list of numbered items. Each numbered item is followed by a drop-down. Select the letter in the drop down that best matches the numbered item with the lettered alternatives. a. Sandstone (Quartz-sandstone) b. Salt c. Limestone d. Potash 1. Sodium (Na) a 2. Calcium (Ca) a 3. Silica a 4. Potassium (K)