It's hard to catch a spark in Horseshoe Fungus without some preparation. Most people char it. There is a thin spongy layer just under the outside layer that some people take out and soak in "strong urine" (potassium nitrate). This will then catch a spark real fast, and burn fairly hot to start your fire.
The fungus you need to find is called Tinder Conch or Tinder Fungus - innonotus obliquus. It grows mostly on Birch trees.
The outside is hard black and kind of spiky. The inside is reddish orange, sometimes with white specks. The inside is the part you need. It will catch a spark without any preparation, right off of the tree. And once your spark catches, it will be be very hard to put out. It will spread throughout the whole chunk.
I hope this helps.
Mike Ameling