Its a very dark green opaque smooth rock, resists stainless knife blade 6.5-7 hardness, its 4x2cm, aprox 40 grams weight. I found this rock among cobble stones in County Roscommon Ireland.Its not large enough to do an accurate density test.Its got yellowish light green, bluish, and some orange spotted color, also some small black spots.Its also got small light colored lines in it.It leaves a clear colorless streak.
I don't think your rock is nephrite. Your rock has a more igneous texture. Nephrite is generally composed of tremolite-actinolite, and/or other serpentine minerals(antigorite, lizardite, Chrysotile, or others) and formed in metamorphic environment under strong pressures. Typically nephrite is usually fine-grained to very fine-grained foliated rock usually of metamorphic origin.
Your rock maybe a diorite igneous rock containing epidote.