first, thanks to all for your answers and help.
So, if I understood well, I have to add HCl to my samples, if there are bubbles, it means that the sample contains CaCO3, what we can check adding phenolthalein and seeing if it turns pink. If there are no bubbles, sample is only CaSO4, which we can check adding BaSO4, generating a precipitate that will not dissolve in dilute HCl. Am I correct?
And my new question is, What concentration is medium concentrate? and dilute? I finished my Chemical Engineering studies 2 years and a half ago and I have been working as a programmer for Accenture (in Barclays Bank!!) and as Technical Support in natural gas operations and as Power Market analyst for Shell, so I have almost forgotten all my knowledge about chemical staff, what it is a shame because I love it!
thanks again and pleased to meet you!