What physical properties are shared by arsenide minerals such as niccolite and skutterudite?

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A labeled diagram of the periodic table entry for arsenic, showing its atomic number 33, symbol As, atomic weight 74.921595, electron configuration, and classification as an other nonmetal. Additional icons indicate arsenic is solid at room temperature, has a rhombohedral crystal structure, and weakly acidic oxides. — arsenic Properties of arsenic.

Arsenide minerals, including niccolite and skutterudite, share several distinct physical characteristics. Regardless of their specific crystal structure or formation temperature, all minerals in this group exhibit the following properties:

Metallic Lustre: They possess a characteristic shiny, metallic appearance.1
Opacity: These minerals are opaque, meaning they do not allow light to pass through them.1
High Specific Gravity: They are relatively dense, characterized by a high specific gravity.1
Hardness: They generally fall into the intermediate to low range on the scale of hardness.1

Structurally, these compounds consist of metals coordinated with arsenic in either octahedral or tetrahedral arrangements, often resembling sulfide minerals.1