Sun dogs, also called mock suns, are colored, luminous spots caused by the refraction of light by six-sided ice crystals in the atmosphere. These bright spots form in the solar halo at points that are 22 degrees on either side of the sun and at the same elevation as the sun. This meteorological phenomenon is also referred to as diamond dust because it forms in nearly clear skies--clear-sky precipitation.
Two Eye Workshop 
I never heard “diamond dust” as another term for sundog. It fits betteer.
What an astonishing photo! Are you always in the right place at the right time? Lucky!