IIQ Raw is a proprietary raw image format developed by Phase One. Structurally, an IIQ Raw image is a valid TIFF image. The actual raw image content is embedded in a TIFF MakerNote tag. Readers that cannot process the contents of this MakerNote tag will read a IIQ Raw image as a regular TIFF. However, such readers will only be able to read the TIFF-compatible image data (usually a lower-quality preview).
There are two variations on the format: a lossless IIQ Large format, and an IIQ Small format, which the Phase One website describes as 'not 100% lossless'.
Since IIQ Raw is structurally identical to a TIFF, magic-based identification tools like Unix file and Apache Tika identify these files as
image/tiff. Exiftool is able to correctly identify the format: