"Sagenitic" quartz is a familiar name for quartz included with acicular rutile, though in this case, the rutile is in the form of these weird elongated strings and sheets of triangular crystals, rather than truly acicular ("hair-like"). At any rate, what you have here is a rare Japanese specimen of this phenomenon. The faces have been polished, as the original crystal may have been coated or damaged and not given a clear window to the fascinating inclusions. This is an old-timer! Ex. Richard Hauck collection.