rock, a rigid, naturally bonded aggregate of geological minerals. A mass of sand or volcanic ash, or a molten lava, would not be be regarded as rock although this is the case in some historical texts; neither would concrete. The solid Earth is made chiefly of rock. Its outermost surface is known as bedrock (see geology), which is generally overlain by a more or less disintegrated zone of subsoil, and then possibly by agricultural soil, although in vineyards such divisions are unusually hazy.
A fragment of bedrock is commonly called a rock or a stone, with more specific names used to indicate its size or smoothness (see geology). The stones seen in many vineyard soils may or may not represent the local bedrock (see alluvium and colluvium). Vines cannot obtain nutrition directly from bedrock or from stones, except by the action of mycorrhizal fungi.