General Citation Information
Catalogers working with facsimiles or microfilms of rare or semi-rare materials (or originals) will often want to cite reference sources for original manuscript. 510 field citation forms for the rare materials community may be found at Standard Citation Forms for Rare Materials Cataloging.
General information on field encoding may be found in the MARC 21 documentation at Citation/Reference note
RISM Citation Information
Music catalogers quite often will cite the Répertoire international des sources musicales (known more commonly as RISM) for these materials. The earlier format of this field referenced the location in the print volumes of the resource. With the gradual shift to an online database, the RISM office has requested that catalogers shift to using the online numbers as the primary reference, with inclusion of the print volume numbers if so desired. Please see the Notes section of the RISM page of Standard Citations Document
In addition, Harvard music catalogers are now following a practice of including a permalink to the RISM record, which will make it much easier for patrons to find the appropriate RISM record. This permaliink may be found in the RISM OPAC record at the link that looks like this: 
This permalink should be present in the OCLC and local records.
Items in RISM OPAC
The correct citation format of the 510 field for these materials is (for example):
510 4_ $a RISM (Répertoire international des sources musicales), $c 00000991016650 $u https://opac.rism.info/search?id=00000991016650&View=rism
with the possible addition of another field for the print volume
510 4_ $a RISM (Répertoire international des sources musicales), $c A/I, CC 4411
Items in RISM Print Volume Only
If you are citing an item for which there is no online presence, you would simply cite the print volume, for example:
510 4_ $a RISM (Répertoire international des sources musicales), $c B/II, page 87
Questions? Please contact Anne Adams (Senior Music Cataloger at Eda Kuhn Loeb Music Library), Andrea Cawelti (Ward Music Cataloger at Houghton Library), or Christina Linklater (Keeper of the Isham Memorial Library and Houghton Music Cataloger).