We often refer to Special Collections resources as "primary sources." See the Merriam-Webster Dictionary definition here, commonly used in the humanities. The sciences use a different definition: "information or literature about original research provided or written by the original researcher." These two definitions of primary source are helpful to keep in mind when you're researching how to cite primary sources, especially in science-oriented citation styles like APA.
In the humanities, the term "primary source" describes how a resource can be used, not what a resource is. Any format - photograph, letter, pamphlet, broadside, newspaper, book - can be a primary source.
The correct citation format for a primary source depends on what it is.
For rare books and historic newspapers, citations are no more complicated than they are for contemporary books, journal articles, and newspapers. We'll call these "published" resources.
For photographs, correspondence, and ephemera, citations can be more complicated. We'll call these "unpublished" resources, because they are often (but not always) unpublished.
Many of the resources in Special Collections are cited in the same way you would cite journal articles, books, newspaper articles, or websites.
These include rare books and articles in rare and historic newsletters, newspapers, and magazines - regardless of whether they are part of our Rare Book Collection or our manuscript collections.
Citation styles aren't designed with unpublished primary source in mind, so they can be difficult to use. When in doubt, remember that a citation should help your reader find the item, and try to include the following information: