This is the hard material deposited on teeth people sometimes call tartar. (lbah.com)
Now, I could certainly imagine (I don't know if this is true, but work with me here) that there is some science that the volume of material deposited on the stalagmite is what varies in different climate conditions. (climate-skeptic.com)
Variety of low cost, stable and catalytically active water splitting materials such as Fe2O3 and BiVO4 have poor charge transport characteristics leading to low PEC efficiency.1, 2 Surface plasmon polaritons (SPP) excited in nanopatterned Al concentrate optical fields in the UV and visible ranges, thus enhancing light absorption within few tens of nanometers of semiconducting material deposited over the Al substrate. (h2awsm.org)