Hi and thanks for posting!
You have an authentic early 19th century Masonic flask - it is listed in the McKearin flask charts as Group 4, either #1, 1a or 2 - I cannot tell from your photos which it is.
One does see these in clear and also moonstone (white milky appearance to glass which is definitely in the glass and not stain) Either of these colors is considerably scarcer than the most common aqua for this mold.
These flasks were blown at the Keene Marlboro Street Glass Works in Keene New Hampshire. Assuming there is no damage, and even minor flaws have a large affect, I would value this in the $1000-1500 range
Other, rarer colors can be worth considerably more!