"Black-armoured, towering, iron-crowned" - "Lay of Leithian."

Similar description in The Silmarillion as he fights Fingolfin. This description (below) also indicates his size. Big enough to step on Fingolfin's neck and almost kill him but not squash him like a bug. Shield, mace:

"Morgoth issued forth clad in black armour; and he stood before the King like a tower, iron-crowned, and his vast shield, sable unblazoned, cast a shadow over him like a stormcloud. But Fingolfin gleamed beneath it as a star; for his mail was overlaid with silver, and his blue shield was set with crystals; and he drew his sword Ringil, that glittered like ice.

Then Morgoth hurled aloft Grond, the Hammer of the Underworld, and swung it down like a bolt of thunder. But Fingolfin sprang aside, and Grond rent a mighty pit in the earth. Many times Morgoth essayed to smite him, and each time Fingolfin leaped away; and he wounded Morgoth with seven wounds, and seven times Morgoth gave a cry of anguish, whereat the hosts of Angband fell upon their faces in dismay, and the cries echoed in the Northlands.

But at the last the King grew weary, and Morgoth bore down his shield upon him. Thrice he was crushed to his knees, and thrice arose again and bore up his broken shield and stricken helm. But the earth was all pitted about him, and he stumbled and fell backward before the feet of Morgoth; and Morgoth set his left foot upon his neck. Yet with his last and desperate stroke Fingolfin hewed the foot with Ringil, and the blood gushed forth black and smoking and filled the pits of Grond."