It depends on the age of the mortar.
Today's mortar is made from sand, Portland cement and water. In very cold weather a plasticiser is added.
Prior to about 1900 mortar was made from sand, lime...
It depends on the sand itself, if it contains silt ( mud), or it contains sulfates , both will crack the mortar , usually in Iraq its one part of cement to 2.25 parts of sand in middle and south of...