Resonant frequency in parallel
XL and XC cancel each other in a series resonant circuit but in parallel resonance they produce an infinite impedance.

XL is jwL and 

XC is 1/jwC 

In parallel they form this impedance: -

Z = \$\dfrac{j\omega L \cdot \frac{1}{j\omega C}}{j\omega L +\frac{1}{j\omega C}}\$

Z = \$\dfrac{j\omega L}{1-\omega^2LC}\$

When \$\omega^2 LC =1\$, the denominator is zero therefore the impedance is infinite.