**5. Crystal Growth Techniques**

Konopacka-Łyskawa [10] reviewed the state of the art of the vaterite crystallization techniques. Vaterite is known to be the least thermodynamically stable anhydrous calcium carbonate polymorph, very rarely found in nature. However, synthetic vaterite has large potential in pharmacology and manufacturing. Well-known classical and new methods used for vaterite precipitation were discussed with particular attention to the parameters affecting the formation of spherical particles.

Tang and Yi-Liang [11] revealed that specific geochemical microenvironments and the bacterial activities in the long-lived volcanic hot springs from Kamchatka result in the development and preservation of the complex pyrite crystal habits. Application of similar techniques to other systems may help in the identification of biogenic iron sulfides in sediments on Earth and other planets.

**Funding:** This research received no external funding.

**Acknowledgments:** As the Guest Editor, I would like to acknowledge all the authors for their valuable contribution to this Special Issue, which is expressed in fascinating and inspiring papers.

**Conflicts of Interest:** The author declares no conflict of interest.
