Eutectic
The eutectic is a mixture of two or more elements which has a lower melting point than any of its constituents.The term is often used in metallurgy to describe an alloy with a well-defined melting point. When a non-eutectic alloy freezes, one component of the alloy crystallizes at one temperature and the other at a different temperature. With a eutectic alloy, the mixture freezes as one at a single temperature. The graph of melting point versus concentration bends at the eutectic, usually with the eutectic being a minimum.
Typical usage: eutectic alloys for soldering in the electronic industry, composed of tin (Sn), lead (Pb) and sometimes silver (Ag).
In steel, iron and carbon react to form iron carbide. Iron and iron carbide, in turn, precipitate out into eutectic crystals. So mild steel is made of grains of iron and of eutectic and harder steel has grains of eutectic and of iron carbide. -- from my hazy recollection of high-school metalwork.
You can see a macroscopic eutectic crystal by freezing a water/alcohol mix in a household freezer. I have made crystals 3 or 3 cm in size, made from leaves of water ice separated by liquid alcohol. I was attempting to fortify some home-brewed mead at the time.
See also: