Today I learnt that chocolate tempering works by controlling the temperature to ensure the crystals set to one (type V) of the six polymorphs.
What do these polymorphs actually look like? By that I mean: what is the crystal structure? Also, what gives type V its properties?
To tackle the question of why form V is shiny, here a physicist refers to the shininess being attributed to
long, skinny molecules all stacked nicely in line—which produces the clean, reflective surface
Digging deeper than this article, I found a publication which analyzes the effect of smaller crystalline structures in form V and refers to the smaller structures allowing for softer form V chocolate, possibly implying that large crystalline structures in form V cause its rigid structure.
Reference
New Textures of Chocolate Are Formed by Polymorphic Crystallization and Template Effects: Velvet Chocolate Laura Bayés-García, Teresa Calvet, Miquel Àngel Cuevas-Diarte, Enric Rovira, Satoru Ueno, and Kiyotaka Sato Crystal Growth & Design 2015 15 (8), 4045-4054 DOI: 10.1021/acs.cgd.5b00660 /acs.cgd.5b00660
The actual polymorphic compound is the fat (cocoa butter). They pure phases will all look like white powders and the 'bloom' referred to in your diagram is white cocoa butter extruded by the solid chocolate, and probably the most obvious visual difference.
The melt-in-your mouth aspect of Form V is going to be because of its appropriate melting point w.r.t your mouth temperature. The decrease in mechanical stability as the melting point decreases is fairly typical of solids (think of plastics softening as you heat them up).
Afraid I don't know why Form V is shinier.
C.f. https://www.sciencedirect.com/science/article/pii/S0969806X04003019
