It's normal fine kitchen soda. Half a teaspoon in a few CC normal hot tapwater. Bring it on a microscopeglass and let it rest for a couple of hours. Sometimes you get very nice white rozets of crystals. Gives not so much pola colors but very nice crystals.
That would be sodium hydrogen carbonate aka sodium bicarbonate but its not sodium carbonate. Sometimes I'd drink baking soda for heartburn and I often notice feather-like crystals on the glass. I didn't know its anisotropic.