Ground quartz (silica) 
Quartz crystal (silicon dioxide, SiO2) ground into a very fine powder.
Characteristics
- Quartz is one of the most abundant minerals in the Earth's crust.
- It has a hardness of 7 on the Mohs scale: it is ground in a cast-iron mortar or on a glass plate.
- In biodynamics it is the basis of preparation 501 (horn silica).
Role in the preparation: The powder is moistened, packed into a cow horn and buried over summer.
Caution: Crystalline silica dust is hazardous to inhale: grind it wet and wear an FFP2 (or higher) mask.
Sources: Quartz - Wikipedia · Biodynamic agriculture - Wikipedia
Documentary information: this is neither a recommendation for use nor a plant-protection or veterinary claim. Check your country's regulations before any use.