unsupervised learning for distribution of outliers

[dervast]

Hi all,
I have two questions related to unsupervised learning.

1. How I can try a few unsupervised learning algorithms and get a measure on the purity of the classification. How clear in other words the found clusters are and how accurately describe the phenomena?

2. Which is the unsupervised algorithm that can capture this type of peaks in the data set? So the data points that seem to be moving out from the main body where all the other points are.
Can you provide some help for a clustering technique that can work with 3 dimensional data?
I had to upload my picture here:
https://postimg.cc/3y2jx5xR


Thanks a lot for your reply.
Regards
Alex