XLSX File type cant be blocked/allowed separately like any other file type.
The XLSX file type is primarily associated with 'Excel' by Microsoft Corporation. This is the new format for Microsoft Office documents. It is a combination of XML architecture and ZIP compression for size reduction (basically means that still carries compression after you unzip it). Microsoft Excel 2007 uses zip compression within is native xlsx file format.
If wanted to allow/block, we need to take XLSX as .zip file since its an archive of .ZIP