I doubt that it is solid limonite (could be a surface film). Two most likely are ankerite and feldspar (scratch it - ankerite is a carbonate and much softer than feldspar which is a silicate, ankerite will fizz with hydrochloric acid but feldspar will not). Ankerite is actually white inside, so try crumbling a few pieces or digging at the surface with a pocket-knife blade point - with feldspar the colour goes right through it. Ankerite is a carbonate mineral with a small iron content, and it also has very good planar cleavage planes (feldspar also has good cleavage planes). However near the ground surface water penetrates the cleavage planes, and in the case of ankerite it slightly oxidises the iron in the mineral to form a very thin yellowish-brown film on the cleavage plane surfaces, Feldspar has no iron in it so does not do this. Hope that helps - ankerite is the most common carbonate mineral in Victorian quartz veins - feldspar does occur in the veins but is far rarer than carbonate minerals.
Leave it for you Jethro - in your dreams mate! Not lack of interest but easier to make a good steady living on pay for a geo than detecting (but many do, especially in mining slumps).