My response may be super late, but I also have the same potting mix from my regular potting mix supplier. At first I also wondered what the gold flakes are, they look pretty and shiny. I used them anyway and they were great on my seedlings and young plants. I asked the seller what the mix is composed of and here is what she said:
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She said the gold flakes are fine grade vermiculite, and they appear like silvery-gold flakes, if not light grayish-brown in color. She said that this type of mix is better for starting seeds because the vermiculite helps retain more moisture.
