This loss is, of course, felt most keenly by students, staff and alumni, whose formative years and daily lives have been shaped by Charles Rennie Mackintosh’s vision.
But the news has reverberated around the globe, for the building represents an almost unattainable dream of a historic structure that still feels experimental, that meets its purpose and is fiercely loved by passing visitors and locals alike.
It is a building whose symbolism combines the flourishing of nature, the giddy rush of spring flowers, with the reassuring solidity of a brooding fortress.
Viewed from Sauchiehall Street, the Mackintosh is all Scots vernacular and stern; face-on, the building is daring, outward-looking and still fresh.
When the daring young architect built it, he meant its inhabitants to feel both risk-taking and reassured. Inside, that is reflected in the contrast between darkness and light, dim corridors and bright studios, the steep steps that open up into the dazzling light of its glazed and top-lit spaces.
Tragically, for now, the lightness, the detail and the nuance of the interiors have been partly consumed.
Anyone who has ever climbed the steep stairs and swung open the Mackintosh’s doors will have known the thrill of placing your hand on a polished brass fingerplate engraved with the single word “Art” and wondering whose fingertips have been there before you.
Recently voted by Riba as the most important architectural work in the UK of the past 175 years, the building is many things: an architectural masterpiece, a global icon, a tourist draw.
But above all, the Mack had remained a working building for fine-art students and, despite its architectural status, was never mothballed or turned into a frigid museum.
In 2012, Glasgow artist Claire Barclay who studied at GSA, described being a new student in 1986, “dizzy with the atmosphere and history of the place”.
I’ve lost count of the artists who have told me that the sense of history and world-class ambition that the building represented helped shape their own self-confidence.
But, for the moment, it feels like not just the art school, but a far wider community and the city of Glasgow itself has lost its beating heart.
The building’s key historic features include its lofty loggia, the Hen Run, where you felt you were on top of the world.
There is the library, which was world famous and the building’s undoubted masterstroke, a place where, embraced by dark wood and bathed by burnished lamps, knowledge seemed to glow.
The Mackintosh Museum, a slightly unwieldy exhibition space, was used daily and, had disaster not struck, would have hosted the forthcoming degree shows for a lucky few students.
In Scotland and far beyond, the building is loved and respected. We can, we should and we must restore the interior.
But while the loss of the library would be a heritage disaster, it is also the loss of the little things that will be hard to bear – the patina of the building, the thousands of handprints that polished the surfaces, the worn wood on the doors where they were scuffed by careless feet, the tiny remnants of the scratched graffiti in the lecture theatre, what Barclay called “the physical marks it bears of generations of artistic endeavour”.
As we struggle to come to terms with the devastation, we must remember Charles Rennie Mackintosh’s true legacy.
We should treasure not just the heritage, the lasting beauty he bestowed by building an unlikely masterpiece on Garnet-hill, but the significance of his youth, the sharpness of his intellect and experimentation.
The true importance of the Mackintosh Building is that its architect bestowed upon a practical working building all the love, knowledge and intimate care that he could muster.
It was not built for royals, for collectors or patrons, for rich folk or pompous city fathers, but to nurture young people and to create artists. We must look to the welfare of students and staff and honour that living tradition as we mark and make amends for a heartbreaking loss.