Loam (from Middle High German leim, like “glue”, from Middle High German līm, belonging to an Indo-Germanic root *lei-, “slimy, slippery soil, brush over something”) is a mixture of sand (grain size > 63 µm), silt (grain size > 2 µm) and clay (grain size < 2 µm). It is formed either by weathering from solid or unconsolidated rocks or by unsorted deposition of the named components. Depending on their formation, a distinction is made between mountain loam, slope loam, boulder clay (glacial), loess loam (loess) and alluvial loam (from river deposits). Clay is widespread and readily available; it represents (burned or unburned) one of the oldest building materials.