All in all, I like Harold's method. It's the old KISS method. No matter how small it is, you should be able to try and flatten it by tapping it once with a small clean smooth hammer on a piece of clean smooth steel. Be careful or you'll lose it. Very small pieces are likely to stick to the face of your hammer. Hit it once, fairly gently, keeping the hammer face on the steel. Then tilt the face very slowly and look at it. You may have to tap it again. If you can't see what has happened, before and after, use a magnifier. I have flattened .0001 gram assay beads and I would bet that they were smaller than your pieces. I could barely see them, even when I had good eyes.
If you have the chemicals, you could put a piece of it in an empty clean vial and add a drop of aqua regia. You may have to put the bottom of the vial in a glass of hot tap water to get it going. After a minute or two or three, add a drop of stannous chloride test solution or a small crystal of stannous chloride. If gold is present, the solution will turn purple or, if a lot has dissolved, it may turn black. Note that this test only tells you if gold is present. If too much silver is in the gold, nothing may dissolve and the test will show no color. If the piece immediately reacts vigorously in the acid, you may have pyrite but, I would test it anyway. Pyrite will give off a sulfur smell in the acids. Don't put your nose over the vial. To smell it safely, wave the fumes, with your hand, towards your nose. You could instead use hydrochloric (muriatic) acid and bleach (definitely warm the vial in the hot water), if you don't have nitric for the aqua regia. However, it will take longer to dissolve.
You could also make a mark with the piece on a touchstone and test it with test acids.
If you don't like the hammer idea and, if you don't have any of the chemicals, I don't know what to tell you. Maybe someone else has some other ideas.
I thought of something else. If you have a microscope or a strong magnifier, look to see if it is well rounded on the edges. If it is, it could likely be gold. Nuggets don't have sharp edges or facets. They've been bouncing around in the water, over the eons, and this rounds them.