[7]: 28 Montbrayite forms small segregations, rarely exceeding 3–5 mm, the mineral is dense, usually homogeneous, very brittle, the fracture is flat-conchoidal, sometimes discontinuous separation is observed.

[4]: 20–21 The mineral formula was initially defined as Au2Te3[4]: 20  or (Au,Sb)2Te3,[1] but more accurate analyses revealed that in different cases constant impurities are part of the montbrayite.

When exposed to HNO3 (in a 1:1 dilution), a kind of etching occurs, it boils strongly, bubbles form and yellow-brown spots of released gold remain on the surface of the mineral.

[8]: 239  With more saturated nitric acid (dilution 3:2) the reaction is less violent, the stain is light brown and small round halos are formed, also colored light brown; with concentrated nitric acid it boils weakly, and the surface is colored uniformly grayish-brown; round halos are not observed.

[4]: 21–22 Calaverite and montbrayite are among the earliest tellurides to form; they have relatively high microindentation hardness values, increased relief, and a pronounced tendency toward idiomorphism and the formation of coarse-crystalline varieties.

[7]: 39 Montbrayite is a typical mineral of tellurium-gold deposits, closely associated with native gold, petzite, altaite, coloradoite, melonite and tellurobismuthite, forming rounded inclusions and veinlets in tetrahedrite and chalcopyrite.

[10]: 106 In the Robb-Montbray mine, montbrayite was found in association with native gold, tellurobismuthite, altaite, petzite, melonite, chalcopyrite, pyrite, sphalerite, chalcocite and marcasite.

[12]: 293  The first samples were found in close intergrowth with altaite, where montbrayite formed as a «shirt» on segregations of native gold of very high purity, 970.