Normal Mixtures is one of four platforms that JMP provides for clustering observations. For a comparison of all four methods, see Overview of Platforms for Clustering Observations.
If you suspect that you have multivariate outliers, you have two options. You can use an outlier cluster or you can select the Robust Normal Mixtures method. The outlier cluster option assumes a uniform distribution and the Robust Normal Mixtures option uses a robust method for estimating the parameters. These methods are less sensitive to outliers than the Normal Mixtures method. For details, see Outlier Cluster and Additional Details for Robust Normal Mixtures.