I would say it depends on where your travertine is from. Travertine is carbonate rock and may be associated with hot springs and caves. From a geochemical perspective is is common to find other elements besides calcium carbonates. If was formed due to hot springs there could be a host of other minerals in the rock, for instance brown banding is sometimes reflective of high iron content. Here is an example from Yellowstone.
Average chemical composition of travertine from Mammoth Hot Springs (table 4)
[SIZE=-1][Average of ten analyses reported by Clarke (1904)][/SIZE]
[TABLE="align: center"]
[TR]
[TD="colspan: 3"]
[/TD]
[/TR]
[TR]
[TD="align: center"]Chemical
constituent[/TD]
[TD="align: center"]Chemical
formula[/TD]
[TD="align: center"]Percentage
composition
[/TD]
[/TR]
[TR]
[TD="colspan: 3"]
[/TD]
[/TR]
[TR]
[TD]Silica[/TD]
[TD]SiO
2[/TD]
[TD="align: right"]0.15[/TD]
[/TR]
[TR]
[TD]Aluminum oxide[/TD]
[TD]Al
2O
3[/TD]
[TD="align: right"].15[/TD]
[/TR]
[TR]
[TD]Iron oxide[/TD]
[TD]Fe
2O
3[/TD]
[/TR]
[TR]
[TD]Calcium oxide[/TD]
[TD]CaO[/TD]
[TD="align: right"]54.20[/TD]
[/TR]
[TR]
[TD]Magnesium oxide[/TD]
[TD]MgO[/TD]
[TD="align: right"].46[/TD]
[/TR]
[TR]
[TD]Potassium oxide[/TD]
[TD]K
2O[/TD]
[TD="align: right"].20[/TD]
[/TR]
[TR]
[TD]Sodium oxide[/TD]
[TD]Na
2O[/TD]
[TD="align: right"].18[/TD]
[/TR]
[TR]
[TD]Water[/TD]
[TD]H
2O[/TD]
[TD="align: right"]1.22[/TD]
[/TR]
[TR]
[TD]Sodium chloride[/TD]
[TD]NaCl[/TD]
[TD="align: right"].25[/TD]
[/TR]
[TR]
[TD]Potassium chloride[/TD]
[TD]KCl[/TD]
[TD="align: right"].08[/TD]
[/TR]
[TR]
[TD]Sulfur trioxide
[/TD]
[TD]SO
3[/TD]
[TD="align: right"].89[/TD]
[/TR]
[TR]
[TD]Carbon dioxide[/TD]
[TD]CO
2[/TD]
[TD="align: right"]42.25[/TD]
[/TR]
[TR]
[TD]Organic carbon[/TD]
[TD]C (organic)[/TD]
[TD="align: right"].20[/TD]
[/TR]
[TR]
[TD]Organic hydrogen[/TD]
[TD]H (organic)[/TD]
[TD="align: right"].02
[/TD]
[/TR]
[TR]
[TD] Total[/TD]
[TD][/TD]
[TD="align: right"]100.25
[/TD]
[/TR]
[/TABLE]
I would say use at your own risk.