## Common ground
All options refer to calcium carbonate, a chemical compound used in various industrial, medical, and food applications.
## Options at a glance
**2106.90 – Food-grade use**
- **Defining trait:** Specifically intended for use in food preparation or as a food additive.
- **Typical examples:** Calcium carbonate added to fortified foods, dietary supplements, or baking powder.
- **Best fit when:** The product is marketed, labeled, or used directly in food or beverages.
**2836.50 – Carbonate classification**
- **Defining trait:** Classified by chemical type—specifically as a carbonate compound—regardless of source or use.
- **Typical examples:** Precipitated calcium carbonate (PCC) used in paper, plastics, or coatings.
- **Best fit when:** The product is defined by its chemical nature and production method (e.g., synthetic precipitation), not end-use.
**2845.90 – Isotopic form**
- **Defining trait:** Contains the stable isotope carbon-13 (¹³C), used in scientific or medical tracing applications.
- **Typical examples:** Tracer compounds in metabolic studies, breath tests for H. pylori infection.
- **Best fit when:** The product is labeled or specified as calcium carbonate with enriched ¹³C.
**3824.99 – Finely ground natural form**
- **Defining trait:** Derived from natural sources (e.g., limestone) and processed to fine particle size, often for industrial fillers.
- **Typical examples:** Filler in rubber, paint, or construction materials.
- **Best fit when:** The product is naturally sourced and ground to a fine powder for non-food, non-isotopic applications.
## Key differences
| Option | Primary trait | Source | Use case | Isotope |
|-------|----------------|--------|----------|---------|
| 2106.90 | Food application | Any | Food additives | No |
| 2836.50 | Chemical classification | Synthetic or natural | Industrial chemicals | No |
| 2845.90 | Isotopic enrichment | Natural or synthetic | Scientific/medical tracing | Yes (¹³C) |
| 3824.99 | Physical form & origin | Natural, finely ground | Fillers, coatings | No |
## How to choose
- Is the product used in food? → 2106.90
- Is it enriched with carbon-13 (¹³C)? → 2845.90
- Is it produced via precipitation (PCC) or chemically defined as a carbonate? → 2836.50
- Is it naturally sourced and finely ground, but not for food or isotopes? → 3824.99
## Overlaps & pitfalls
- A product can be both **finely ground natural** (3824.99) and used in food (2106.90), but the primary use determines the code.
- **Precipitated calcium carbonate** (2836.50) may also be used in food, but only if specifically labeled for that purpose.
- If multiple traits apply, prioritize based on **main function**: food use > isotope > chemical classification > physical form.
- Do not assume "finely ground" implies industrial use—context matters