Cuts · Platonic solids

Octahedron

3D model · 8 faces · 10 mm circumsphere

Eight equilateral triangles, meeting four at each of six vertices, dual to the cube. It is the shape rough diamond most often grows in, and spinel and magnetite share the habit.

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About the octahedron

Eight equilateral triangles, meeting four at each of six vertices, dual to the cube. It is the shape rough diamond most often grows in, and spinel and magnetite share the habit.

It is also where the brilliant began. The single cut is an octahedron with the top point sawn off for a table and the corners bevelled, and every brilliant since descends from it.

See the Old Single, rebuilt in our historic cuts.

Octahedron specifications

Taken from the delivered model and checked against its mesh every time this page is built.

CategoryPlatonic solids
Faces8 equilateral triangles, all congruent
Vertices6, 4 faces meeting at each
Edges12, each 7.071 mm
Schläfli symbol{3,4}
DualThe hexahedron (the cube)
Dihedral angle109.471°, the same on every edge
Size8.165 x 7.071 x 5.774 mm, resting on a face
Circumsphere10.000 mm across, through every vertex
Midsphere7.071 mm across, touching every edge
Insphere5.774 mm across, touching every face
Surface area173.21 mm²
Volume166.67 mm³
Sphere fill31.8% of its circumsphere
Isoperimetric quotient0.605 (a sphere is 1)
Weight at this size2.93 ct in diamond, 2.68 ct in moissanite
OrientationMillimetres, Y up, one face resting on the ground plane, centred on the Y axis
FilesSTEP, 3DM, STL, OBJ, FBX, GLB. 3D files only, no cutting files

Octahedron: questions

What files come with the Octahedron 3D model?

Six formats: STEP (the exact solid for CAD), 3DM for Rhino, STL and OBJ meshes, FBX for Blender, 3ds Max, Maya, Cinema 4D, Unity and Unreal, and GLB for the web and AR. All are in millimetres at real-world scale, with 8 flat faces.

Is there a cutting file for the Octahedron?

No. The Platonic solids are sold as 3D models only, with no faceting design, tier table or diagram.

How big is the Octahedron model?

It measures 8.165 x 7.071 x 5.774 mm resting on a face, with every vertex on a sphere 10 mm across. All five Platonic solids share that sphere, so they nest and sit together at true relative size. Scale it uniformly to any size: for a 10 mm edge, scale by 1.4142.

How is the Octahedron model oriented?

Y up, with one face resting on the ground plane and the centroid on the Y axis. The midpoint of one edge of the resting face lies on the +X axis, which keeps the cube square to the axes.

Can I 3D print or cast the Octahedron model?

Yes. The mesh is watertight and manifold, with outward normals and no duplicate vertices, so it prints and casts without repair. Use the STEP file when you need the exact solid in CAD.

More Platonic solids

Get the Octahedron files

6 formatsMillimetresWatertight

Octahedron 3D files

The octahedron as exact geometry: 8 flat faces, real-world scale, ready for CAD, rendering, printing and casting. The Platonic solids are sold as 3D files only.

  • STEPExact faceted solid for CAD
  • 3DMRhino, closed mesh on its own layer
  • STLWatertight mesh for printing and casting
  • OBJMesh for modelling and rendering
  • FBXBlender, 3ds Max, Maya, Cinema 4D, Unity, Unreal
  • GLBWeb, AR and quick previews
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