In the data dictionary, you can find several views that provide useful information about the indexes in your database. It is important to note that some of the information may be available only after you have analyzed the indexes.
DBA_INDEXES provides information on the indexes themselves. You can use this view to find particular types of indexes (bitmapped, functional, B-tree).
DBA_IDN_COLUMNS provides information on indexed columns indexed. You can use information from this view to list the columns that are indexed by each index, including those that participate in concatenated indexes.
DBA_IND_EXPRESSIONS provides information on index expressions or function-based indexes.