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We present the first nonlinear results on the problem of non-rotating thermal convection in an internally heated full sphere. A nonlinear stability analysis by the energy method yields that, at least for no-slip boundary conditions, the critical Rayleigh numbers for linear stability and nonlinear stability coincide. We then explore different ranges of the parameter regime using direct numerical simulations. We first report on the system behaviour for a fixed Prandtl number of unity and both stress-free and no-slip boundary conditions up to very high forcing, reaching Rayleigh number 
$Ra=2\times 10^{12}$, approximately 250 million times the critical value (
$Ra_c$) for the onset of convection under no-slip conditions. For both boundary conditions, we observe a scaling for the advective heat transfer measured by the Nusselt number 
$Nu$ close to 
$Nu \sim Ra^{1/4}$. This is consistent with a scaling prediction that we formulate analogously to the classical scaling in Rayleigh–Bénard convection. We then investigate the Prandtl number dependence at low to intermediate forcing for stress-free boundary conditions in the ranges 
$0.1 \leq Pr \leq 30$ and 
$Ra_c=3091\leq Ra \leq 3\times 10^5 \approx 100Ra_c$. We find five distinct dynamical regimes depending on the Prandtl number, describe each regime individually and issue heuristic interpretations of the system behaviour where possible.
The new mineral yellowcatite (IMA2024-030), KNaFe3+2(Se4+O3)2(V5+2O7)·7H2O, was found underground in the School Section #32 mine, Grand County, Utah, USA, where it is a secondary, post-mining phase occurring on montroseite-corvusite-asphaltite-mica-bearing sandstone in association with barnesite, gypsum and mandarinoite. Crystals are thin hexagonal plates, up to ∼0.2 mm in diameter. Crystals are yellow and transparent, with vitreous to pearly lustre and pale-yellow streak. The mineral is brittle with curved fracture and two cleavages: perfect on {001} and good on {100}. The Mohs hardness is ∼2. The measured density is 2.79(2) g·cm–3. Optically, yellowcatite is uniaxial (–) with ω = 1.910(5) and ε = 1.740(5) (white light). The mineral is pleochroic with O yellow and E colourless; O > E. The empirical formula is (K0.65□0.35)Σ1.00(Na0.66Mg0.30)Σ0.96Fe3+2.02Se4+1.99V5+2.01O20H14.02. Yellowcatite is hexagonal, space group P
$\bar 6$m2, with cell parameters: a = 5.4966(7), c = 17.2109(16) Å, V = 450.31(13) Å3 and Z = 1. In the crystal structure of yellowcatite (R1 = 5.12% for 281 I > 2σI reflections), Fe3+O6 octahedra, Se4+O3 pyramids and V5+O4 tetrahedra link by corner-sharing to form sheets similar to those in the well-known merwinite structure, but with the apices of the Se4+O3 pyramids in the ‘pinwheels’ pointing in the same direction as the V5+O4 tetrahedra. The unshared vertices of the V5+O4 tetrahedra in adjacent sheets link to one another to form divanadate groups, thereby joining two sheets into a double-sheet slab structural unit. Between adjacent slabs is a layer of unlinked Na(H2O)6 coordinations that are presumed to represent octahedra exhibiting rotational disorder.
