Amalgam means a combination of diverse elements. Amalgamation is sometimes used in the same sense—and dictionaries list it as a variant of amalgam—but today it’s often used to refer to the act of combining diverse elements. So an amalgam is created through amalgamation.
Examples
In these examples, amalgam denotes the combination resulting from the mixture of diverse elements:
Unlike Tunisia and Egypt, Libya as a country is actually an amalgam of about 140 tribes and clans. [NPR]
Marcel had tried to evoke the amalgam of America and 17th-century France that has made such an indelible impression on this enigmatic corner of rural Louisiana. [Telegraph]
Anyone with an ability to turn on a television set knows that the Tudor rose was an amalgam of the white and red rose factions from the dynastic war. [New Zealand Herald]
In these examples, amalgamation refers to the act of mixing diverse elements:
Coburn was mayor of Cumberland in pre-amalgamation Ottawa for about a decade. [Ottawa Citizen]
The greatest legends, the supreme myths, are founded on an amalgamation of opposites. [Washington Post]
The amalgamation in August last year made SNH the Scottish government’s statutory adviser on deer. [BBC News]
And in these sentences, amalgamation would bear replacement with amalgam:
Swisher also was an amalgamation of 93 franchisees all working out of their trucks. [Forbes]
Modigliani’s art is a timid amalgamation of primitivism, African masks, Cycladic idols, the machine aesthetic, Art Nouveau and Old Master paintings. [Wall Street Journal]