That is the good stuff ! I look forward to this style of mold in my garden as I am an organic grower, an these lil dudes are required to help break that organic material down and make it available to the plant. Mycelium are literally...fungus roots. Most organic soils and mixes come ripe with Mycelium in them. If it starts to turn from that pretty white, into a brown/black/slimy looking thing, then its not the good kind.