## 2 Types and Properties of Calcium Carbonate Particles  
In general, there are two sources of CaCO\({}_{3}\), one is ground calcium carbonate (GCC) and another one is precipitated calcium carbonate (PCC) [8], chalk, or marble. While the PCC is present as crystals and exists in three polymorphs, i.e., calcite, aragonite, and vaterite. Though they have several identical properties still they vary in the following manner as shown in Table 1. While all the PCC types of polymorphs are differentiated above in the Table 2.  
Calcium based particles has drawn their attention towards different scientific filed in the last decade due to their diversity in morphology, biocompatible in nature, economical, and non-toxic effect on the environment [27]. Since the calcium is already present in our body, microbes, plants, etc., it does not have a detrimental effect on any of these species, so it is considered as superior particles, in comparison to other metal oxide particles. Such as, ZnO, TiO\({}_{2}\), etc., are photo catalytic in nature, whereas CuO, CoNPs, etc., are toxic due to their heavy metal nature. These metals oxide particles persists in nature for much longer  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**S. No.** & **Calcite** & **Aragonite** & **Vaterite** & **References** \\ \hline
1. ThermalStability & Thermodynamically most stable & Moderately stable & Least stable polymorph & [21] \\ \hline
2. Solubility & - & More soluble and denser than calcite & - \\ \hline
3. Structure & Exists as a trigonal crystalline form in nature & Forms needle-like orthorhombic crystals and formed at higher temperature and pressure & Hexagonal structure and rarely seen in the natural mineral \\ \hline
4. Stability & - & Metastable and slowly gets converted to calcite & & [23] \\ \hline
5. Interaction with water and reorganization & - & - & Vaterite when exposed to H\({}_{2}\)O, slowly dissolves and recrystallizes to a stable form \\ \hline
6. Porosity, surface area & - & - & Large porosity and large surface area \\ \hline
7. Disintegrity & - & - & Rapid disintegration under relatively mild conditions \\ \hline
8. Biocompatibility & - & Biocompatible properties & [21] \\ \hline \hline \end{tabular}
\end{table}
Table 2: Differences between different types of calcium carbonate nanoparticles polymorphs.  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**S. No.** & **Ground Calcium Carbonate** & **Precipitated Calcium Carbonate** & **References** \\ \hline
1. Source & Extracted from earth & Present as crystals in calcite (rhombohedral), aragonite (orthorhombic), and vaterite (hexagonal) forms & [28] \\ \hline
2. Examples & Examples: chalks, marble & - & \\ \hline
3. Processing & Grinding is required either in wet or dry conditions. & - \\ \hline
4. Available in market & - & Commercial PCC was produced in 1841. & \\ \hline
5. Methods for synthesis & Thermolysis & Three common processes for the production of synthetic PCC(1) lime soda process(2) calcium chloride process(3) the carbonation process & [29] \\ \hline \hline \end{tabular}
\end{table}
Table 1: Differences between ground and precipitated calcium carbonate particles.  
time and may show, bio magnification in the higher animals in the food chain. Whereas calcium is already present in almost most of the organisms, so there is already degradation mechanism present in the organism for calcium based particles. The types of calcium carbonate particles are based on their morphology. Calcium carbonate particles (CCPs) are white color powder, insoluble in water but soluble in HCl, biocompatible, pH sensitive, biodegradable, abundant in nature, economically viable, and exhibit polymorphism [27]. CCPs aggregate easily during the process of preparation and disposal [30].