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Hydrochloric acid is what is used to test for limestone, I doubt vinegar will produce much in the way of bubbles. And having specialised in petrography of igneous and metamorphic rocks for a few years I am very confident it is neither of those. The easiest way to recognise a trachyte are the white rectangular plagioclase crystals - I can't see anything remotely resembling those in the pictures. The texture of the veins is purely a secondary mineralisation process.
Still - anyone else here who's brother's lawn is mowed by a guy who lives in the same street as a guy who knew a geologist's sister is just as entitled to an opinion. It's hard to know for sure without holding it - but it ain't a trachyte!
Cheers,
Andrew.
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