ScBCSi (x = 0.52, y = 1.42, z = 1.17 and w = 0.02) has a hexagonal crystal structure with space group Pm2 (No. 187) and lattice constants a = b = 1.43055(8) and c = 2.37477(13) nm. Single crystals of this compound were obtained as an intergrowth phase in a float-zoned single crystal of ScBCSi. This phase is not described in the phase diagram of figure 17 because it is a quaternary compound. Its hexagonal structure is rare and has 79 atomic positions in the unit cell: eight partially occupied Sc sites, 62 B sites, two C sites, two Si sites and six B/C sites. Six B sites and one of the two Si sites have partial occupancies. The associated atomic coordinates, site occupancies and isotropic displacement factors are listed in table X.
There are seven structurally independent icosahedra I1–I7 which are formed by B1–B8, B9–B12, B13–B20, B/C21–B24, B/C25–B29, B30–B37 and B/C38–B42 sites, respectively; B43–B46 sites form the B polyhedron and B47–B53 sites construct the B polyhedron. B54–B59 sites form the irregularly shaped B polyhedron in which only 10.7 boron atoms are available because most of sites are too close to each other to be occupied simultaneously. Ten bridging sites C60–B69 interconnect polyhedron units or other bridging sites to form a 3D boron framework structure. One description of the crystal structure uses three pillar-like units that extend along the c-axis that however results in undesired overlaps between those three pillar-like units. An alternative is to define two pillar-like　structure units. Figure 29 shows the boron framework structure of　ScBCSi viewed along the c-axis, where the pillar-like units P1 and P2 are colored in dark green and light green respectively and are bridged by yellow icosahedra I4 and I7.
These pillar-like units P1 and P2 are shown in figures 30a and b, respectively.　P1 consists of icosahedra I1 and I3, an irregularly shaped B polyhedron and　other bridge site atoms where two supericosahedra can be seen above and below the B polyhedron. Each supericosahedron is formed by three icosahedra I1 and three icosahedra I3 and is the same as the supericosahedron　O(1) shown in figure 24a.The P2 unit consists of icosahedra I2, I5 and I6, B polyhedron and other　bridge site atoms. Eight Sc sites with occupancies between 0.49　(Sc8) and 0.98 (Sc1) spread over the boron framework.
As described above, this hexagonal phase originates from a cubic phase, and thus one may expect a similar structural element in these phases. There is an obvious relation between the hexagonal ab-plane and the cubic (111) plane. Figures 31a and b show the hexagonal (001) and the cubic (111) planes, respectively. Both network structures are almost the same that allows intergrowth of the hexagonal phase in the cubic phase.