Index page uses loop.php template which handles the posts of Gallery Post Format. Single posts use the single.php template. The category.php template doesn’t show galleries of Standard Post Format.
Gallery Post Format is broken in the index.php template for Envira, and Foo, but not in the content-single.php template.
Both index and single pages use content.php template.
Template contact-gallery.php used in both the index and single pages.
Which template is used for the index page? Which template for the single page? However, posts in both index and single pages use the content-gallery.php template.
Index page uses image.php template. Every post is in content.php template, but those of Gallery Post Format get an extra link to an archive.php page.
All posts on index page use content.php template, but responds to Gallery Post Format by changing the entry-title font. The post on a single page uses content-single.php template.
Index and single pages both use the content-gallery.php template (but no special templates for Link Post Format or Quote Post Format).