Strange Miller Index Notation [00.1]

[Abigale]

Do someone knows what this dot "." means?
I just know this notation [001].

Thank u
Abigale

 

[DrDu]

Maybe they mean $[00\bar{1}]$?

 

[Useful nucleus]

This is an old fashioned way to describe directions in hexagonal systems using 3 coordinates. See the first few pages here:

http://www.public.asu.edu/~rosebudx/Chap4_99_131.pdf

In particular page 101.