Question. Sandstone and limestone are both sedimentary rock. Is it possible that a stone could qualify as both limestone and sandstone?

Answer. No. Limestone is a sedimentary rock that is composed primarily of calcium carbonate. Sandstone on the other hand, is a sedimentary rock that is composed primarily of mineral and rock fragments in a range of 2 to 0.06 mil. and having a minimum of 60% free silica. Particles can be cemented or bonded together with various materials including silica, iron oxides, carbonates, or clay. Quartzitic sandstone contains at least 90% free silica (quartz, grains plus siliceous cement).