I'll have a go to set the ball rolling.
Wondering whether the specimen is a rounded bit of rock chipped of an outcrop or whether it is a concretion of sand weathered from an outcrop of the same rock. Either way the composite minerals would be similar.
Hard to be really sure from the photo but the grains in the specimen seem rounded or semi rounded rather than sharp and crystalline so I would guess the latter.
The pinkish tinge at one end could be a pink feldspar or orthoclase, a common mineral in granites and pegmatites. Are there any granites especially pink granite outcrops in the vicinity of the find?
Normally granites are non-magnetic but if it is a cemented granitic sand concretion, it's magnetic property could possibly be due to the binding cement in the concretion being iron rich.
Maybe others more familiar with the Oberon area geology could help here.