6.5% of stony meteorites are achondrites. The achondrites include eucrites (35%), ureilites (14%), diogenites (13%), howardites (10%), lunar (10%), martian (6%), and some rare achondrites (together, 12%). In the absence of a fusion crust, neither you nor I can identify a rock as an achondrite just “by looking” and I think no one else can either. Achondrites are made of the same minerals as terrestrial rocks. The igneous (mostly basaltic) achondrites (some eucrites, some diogenites, some lunar, and most martian) look just like their terrestrial counterparts. They are all formed by the same processes. Many of the breccias look like some kinds of terrestrial sedimentary rocks and I’ve known experienced scientists and collectors who have mistaken brecciated eucrites for lunar breccias. Some brecciated achondrites contain iron-nickel metal, but not much, although in a few it can be seen on a sawn face or as rusty spots. I suspect that only a few brecciated achondrites contain enough metal for the rock to attract a magnet.
It requires sophisticated (=expensive) chemical or mineralogic tests to identify a rock as an achondrite and to identify just which type of achondrite the meteorite is.