I don't believe the vase is alabastro. It isn't Seguso definitely. I believe the glass is the type called opaline veritable, but can't see the characteristics of the glass well in the pictures. This type of glass was made in France, Italy (Nason), Germany, and probably other countries. It looks like the very top of your rim is clear, so that helps some. Nason had a clear ring on their pieces, but it was a bit below the rim instead of on top. So your vase doesn't appear to be Nason. If you put "veritable opaline" into Google, there are many pieces similar to yours, but I didn't see an exact one when I looked briefly.