Haustein
Haustein is a term that generally refers to a type of stone used in construction, particularly for the outer walls or significant structural elements of a house. The specific type of stone can vary greatly depending on the geographical location and local geological availability. Historically, haustein was a common building material in many regions due to its durability and aesthetic appeal. It could be quarried or gathered from riverbeds and fields. The term itself suggests a stone integral to the "house" (Haus) construction.
In some contexts, haustein might refer to rough-hewn or undressed stones, as opposed to finely cut ashlar