there are some astronomical observations that indicate the presence of millimeter-sized cosmic dust grains. Such is the case of comet 67P/Churyumov-Gerasimenko (Fulle et al. 2015, Rotundi et al. 2015), circumstellar disks (e.g., Andrews & Williams 2005; Canovas et al. 2015, 2016; Kataoka et al. 2016), in particular, the circumstellar disk orbiting Fomalhaut and HR 4796A (Kalas et al. 2005, Milli et al. 2017, Min et al. 2010)
reqV=3.9 mm (volume-equivalent sphere radius)
irregular
1.54+i0 (Klein C & Hurbulst CS Jr. Manual of Mineralogy. New York: Wiley, 1993)
Muñoz O, Moreno F, Vargas-Martín F, Guirado D, Escobar-Cerezo J, Min M, Hovenier JW. Experimental Phase Functions of Millimeter-sized Cosmic Dust Grains. Astrophysical Journal, vol. 846, pp. 846-885, 2017