Hydrogen $({\text{H}}_{2})$, deuterium $({\text{D}}_{2})$, and the $0.25{\text{D}}_{2}\text{\ensuremath{-}}0.5\text{DT-}0.25{\text{T}}_{2}$ isotopic mixture of deuterium and tritium (D-T) each form a metastable solid state below their respective triple-point temperatures $({T}_{TP})$. The metastable solid is observed to nucleate and grow from inside of a $5--10\text{ }\ensuremath{\mu}\text{m}$ inner diameter borosilicate glass tube when the liquid hydrogens are slowly cooled through their respective ${T}_{TP}$. These metastable solids have their triple-point temperature 15--43 mK below the stable hexagonal close-packed (hcp) crystal of the same composition, a different growth habit, and recrystallize to the hcp solid. This metastable solid may be a crystal with unknown structure or, less likely, hcp with stacking faults and other defects.