Before adding any data to mindat.org be careful to understand your responsibilities:
Anything you add must be your own copyright - for example with mineral photographs (if you commissioned a photographer to take a photo of your specimen you might NOT automatically have the right to upload that photo to mindat.org - it is your responsibility to check). Similarly, you must NEVER take blocks of text from other websites or books to add into the database.
You must ensure data you enter is as accurate as possible. For photos, ensure the location is entered as accurately as possible, for example, do not put 'Mapimi, Mexico' if you know that the specimen is certainly from the 'Ojuela Mine, Mapimi, Mexico'. If you have suspicions about the accuracy of data, or the accuracy of a mineral identification for example, you must state your concerns when adding the data.
Any data you give must be referenced. For example, you cannot add minerals to a location without a reference. See the References section for further information on how to add references.