Awesome find! It looks like a knife blade to me. I think a dart or arrow point would have some notches, especially during the historic period. I don't doubt it's an authentic glass artifact. They were known for taking the blue and green glass insulators along the rail road, but it could have been a bottle as well. Were there any other chips of glass around? I have come across places where someone was knapping with blue glass, but I have yet to find a point made of it. That is a rare piece indeed!