Uranyl formate (UO₂(CHO₂)₂·H₂O) is a salt that exists as a fine yellow free-flowing powder occasionally used in transmission electron microscopy.

Uranyl formate

Identifiers
CAS Number	16984-59-1 N
3D model (JSmol)	Interactive image
ChemSpider	78394 Y
ECHA InfoCard	100.037.315
PubChem CID	86897
InChI InChI=1S/2CH2O2.2O.U/c2*2-1-3;;;/h2*1H,(H,2,3);;; Y Key: SFIHWLKHBCDNCE-UHFFFAOYSA-N Y
SMILES O=CO.O=CO.O=[U]=O
Properties
Chemical formula	(UO2(CHO2)2·H2O)
Molar mass	378.08 g/mol
Appearance	fine yellow powder
Melting point	110 °C (230 °F; 383 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

It is occasionally used as a 0.5% or 1% aqueous negative stain in transmission electron microscopy (TEM) because it shows a finer grain structure than uranyl acetate. However, uranyl formate does not easily go into solution, and once dissolved, has a rather limited lifetime as a stain. It is quite sensitive to light, especially ultraviolet light, and will precipitate if exposed.