A crystal model has the following characteristics: a single principal axis of four-fold rotational symmetry, two horizontal crystallographic axes of equal length perpendicular to each other, and a ver

Here are the answers to the questions about the crystal drawing:

a) Insert and label the elements of symmetry:

• One 4-fold rotation axis ($C_4$): Vertical, passing through the center of the crystal.
• Four 2-fold rotation axes ($C_2$): Horizontal, two parallel to the $a$-axes, and two bisecting the angles between the $a$-axes.
• Five mirror planes ($m$): One horizontal mirror plane, and four vertical mirror planes (two containing the $a$-axes, and two bisecting the angles between the $a$-axes).
• One center of inversion ($i$): Located at the center of the crystal.

b) Index the faces labelled G, H and J:
G: $\boxed{\text{(111)}}$
H: $\boxed{\text{(100)}}$
J: $\boxed{\text{(010)}}$

c) State, with reasons, the system to which the model belongs.
Crystal system: $\boxed{\text{Tetragonal}}$
Reason(s): The crystal possesses a single principal axis of four-fold rotational symmetry. Its two horizontal crystallographic axes ($a_1$ and $a_2$) are equal in length and perpendicular to each other, while the vertical axis ($c$) is perpendicular to $a_1$ and $a_2$ but of a different length.

d) Which mineral crystallizes in such a habit?
$\boxed{\text{Zircon}}$