He worked a lot with the landscapes of his native Italy, using high degrees of contrast and making these alternately look like fabric draped over a structure, and or else like an abstract and highly graphic composition.
Giacomelli also photographed people, usually, it seems, working in series and exploring a theme, like this astonishing one on priests and seminarists at play.
There seems to be a timeless and poetic side to the movement and superpositions the photographs manage to capture, and his framing enhances this...
And Giacomelli also appears to have immense tenderness for his sujects, who are definitely not the rich and famous of this world...
If you are interested, here are the references of the book:
Mario Giacomelli / The Black is waiting for the White (good title!)
edited by Alessandro Mauro, Contrasto
textes by various authors such as Christian Caujolle, Roberta Valtorta, Paolo Morello etc.