It has to do with porosity of the calcitic travertine. Sometimes inthe hot springs we see an equilibria of silicious 'acid' along with the carbonate solutions so when it sets up nd crystallizes, the crystals are larger nd more porouS, and, less dense. Usually makes em chemically and physically weaker and more prone to erosion.
Trvertine "flowstones" along the bases of the gara will often be much denser and therefore more useful to artsy craftsy uses like counter tops or tiles.
Chalybeate springs are mostly iron carbonates. Even though the word refers to a greek foundryman, the mineral chalybite ( aform of siderite) is one of the principle chemical components.
You a caver?
Ever do Lechuguilla?? You can see a totally different flowstone makeup there. TheArchea and reducing thermal sulfitic springsi hve reduced gypsum deposits leaving hydromagnesite and Sulfur . But its gorgeous.
One of my partners was in there as part of a mapping expedition (I wasnt). Only caving Ive done was in W Va and in Apatite /coquina complexes in florida and that was years ago.