NOVELTY - Crucible (10), comprises (a) a crucible main body (12) comprising a heat-resistant member, and a (b) protective film (14) formed at least on an inner surface of the crucible main body, where the protective film has a composition comprising silicon oxynitride compound.    USE - The crucible is useful for melting silicon (claimed) for the production of mono/poly crystal silicon, which is useful in a semiconductor device and a solar cell.    ADVANTAGE - The crucible: has excellent releasability to a silicon block; reduces the amount of impurities dissolved in a silicon melt; and can be produced at low cost.    DETAILED DESCRIPTION - Crucible (10) for melting silicon comprising (a) a crucible main body (12) comprising a heat-resistant member, and (b) a protective film (14) formed at least on an inner surface of the crucible main body, where the protective film has composition comprising silicon oxynitride compound of formula (SiOxNy) (I).    x, y = greater than 0.    INDEPENDENT CLAIMS are included for:    (1) a release agent for use in forming a protective film formed at least on an inner surface of a crucible for melting silicon, where the release agent comprises a powder of fine particles having the composition on its surface;    (2) a crucible for melting silicon comprising (a) and (b) as above per se; and second solid particles having a composition comprising silicon dioxide and having a particle diameter smaller than a particle diameter of the first solid particles, and where the second particles connect the first solid particles with each other at a part of an interface between the first solid particles; and    (3) a release agent for use in forming a protective film formed at least on an inner surface of a crucible for melting silicon, where the release agent comprises a powder comprising first solid particles having the composition on its surface; and second solid particles having a composition comprising silicon dioxide and having a particle diameter smaller than a particle diameter of the first solid particles.    DESCRIPTION OF DRAWING(S) - The figure shows a sectional view of the crucible.    Crucible (10)    Crucible main body (12)    Protective film. (14)