  We present recent JWST NIRCam imaging observations of SPT0615-JD (also known
as the Cosmic Gems Arc), lensed by the galaxy cluster SPT-CL J0615-5746. The
5-arcsec-long arc is the most highly magnified $z>10$ galaxy known, straddling
the lensing critical curve and revealing five star clusters with radii $\sim 1$
pc or less. We measure the full arc to have F200W 24.5 AB mag, consisting of
two mirror images, each 25.3 AB mag with a magnification $\mu \sim 60$
(delensed 29.7 AB mag, $M_{UV} = -17.8$). The galaxy has an extremely strong
Lyman break F115W$-$F200W $>3.2$ mag ($2\sigma$ lower limit), is undetected in
all bluer filters ($< 2\sigma$), and has a very blue continuum slope redward of
the break ($\beta = -2.7 \pm 0.1$), resulting in a photometric redshift
$z_{phot} = 10.2 \pm 0.2$ (95% confidence) with no significant likelihood below
$z < 9.8$. Based on SED fitting to the total photometry, we estimate an
intrinsic stellar mass of $M_{*} \sim 2.4 - 5.6 \times 10^{7} M_{\odot}$, young
mass-weighted age of $\sim 21 - 79$ Myr, low dust content ($A_V < 0.15$), and a
low metallicity of $\lesssim 1\%~Z_{\odot}$. We identify a fainter third
counterimage candidate within 2.2 arcsec of the predicted position, lensed to
AB mag 28.4 and magnified by $\mu \sim 2$, suggesting the fold arc may only
show $\sim60$% of the galaxy. SPT0615-JD is a unique laboratory to study star
clusters observed within a galaxy just 460 Myr after the Big Bang.
