Detecting Calcite in Rocks

1. Detecting Calcite in Rocks Students add “acid” (white vinegar) to a calcite sample to see calcite’s unique reaction. Students are given four rock samples (basalt, limestone, marble, and sandstone) and are given the problem of identifying which rock sample contains calcite. Students observe that the calcite begins to bubble or “fizz” when it is in contact with the vinegar. Students suggest to investigate the rocks by adding vinegar to the rock samples to see if they react with bubbles of “fizz”. Student samples: Observations of basalt, limestone, marble, and sandstone with the vinegar. Conclusions: Students concluded that the marble and limestone contained calcite due to their observation of bubbles and “fizz” when they added the vinegar. However, some students believed the sandstone contained calcite because there were some bubbles. Other students disagreed because the bubbles were different from what they observed with the calcite. They were asked what other investigations they could do to solve the problem. They suggested an evaporation test using the leftover vinegar in the vial in order to see what is “invisible” (possibly calcite). They accessed their prior experience with an evaporation test earlier in the unit. All suggestions and conclusions that the students created were authentic and related to their observations in the investigation.