Bright sky blue globular crystal aggregtes to 0.5mm and as large patches, veinlets, and crusts. Decrespignyite-(Y) is a yttrium - copper bearing REM and a carbonate. It is according to Mindat composed of individual tiny pseudohexagonal, often curved platelets. It is found at only one locality worldwide.
As noted by the mineral name, Decrespignyite-(Y), contains the rare-earth element yttrium. Major applications of yttrium are extensive and include fluorescent lamps, phosphor compounds in computer monitirs, lasers, lighting applications, abrasives, bearings, and high-temperature alloys amongst others. Recent cost for yttrium oxide in 2019 was $14/lb down from $65/1b in 2011. The main source for yttrium is China, but worldwide reserves are found in Australia, Brazil, and India.