In what types of high-altitude clouds are the necessary ice crystals usually found?
Answer
Cirrus or cirrostratus
The ice crystals required for this optical effect are typically found in high, thin clouds known as cirrus or cirrostratus clouds.

#Videos
What does a moon halo mean for snow chances? - YouTube
Related Questions
What is the scientific name for the luminous ring encircling the moon?What atmospheric components generate the 22° halo?In what types of high-altitude clouds are the necessary ice crystals usually found?By approximately what angle do hexagonal ice crystals refract moonlight to form the standard halo?In a well-formed 22° halo, which color appears on the edge closest to the moon?The presence of cirrus clouds preceding a 22° halo is often the first indicator of what meteorological system?According to the text, what is the relationship between the halo and an approaching storm?How many pinky-finger widths (held at arm's length) span the diameter of a standard 22° halo from bottom to top?What caution is necessary when attempting to observe a solar halo?What is the angle associated with the rarer halo mentioned, which appears much further out from the sun or moon?What is the general geometric shape of the ice crystals responsible for forming the common halo?